JPH114533A - Digital protection relay - Google Patents

Abstract

(57) [Summary] PROBLEM TO BE SOLVED: To surely disable a transformer inrush current and to operate reliably in the event of a transformer internal accident. SOLUTION: An alternating current from a protected object is input, sampled and converted into a digital amount to obtain a differential current. When an electric amount based on the differential current is equal to or more than a predetermined value, an internal accident occurs. a digital protective relay comprising a first determining means for determining that there is, among the determined differential current, digital amount of K instantaneous value of the electrical angle T of intervals (i _m, i _{m -1} , im _-2 , im _-3 , ...,
i _{m− (K−1)} ), and the amplitude value in a certain section of the differential current is obtained by the following amplitude value calculation equation (a). Whether the obtained amplitude value is equal to or less than the certain value is determined. A second judging means for judging whether or not the value is equal to or less than a predetermined value, and an exciting rush current countermeasure element having a first restoring delay means for restoring the output of the second judging means for a predetermined time are provided. [Equation 71]

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a digital protection relay used for protection of a power system, for example, a transformer.
The present invention relates to a digital protection relay that operates reliably in the event of a transformer internal accident.

[0002]

2. Description of the Related Art FIG. 30 is a circuit diagram showing an example of a configuration in which a digital differential relay (hereinafter referred to as a differential relay) for protecting a transformer of this type is applied to a power transformer. In FIG. 30, a power system power supply G includes a circuit breaker CB.
, A power transformer (hereinafter simply referred to as a transformer) Tr to be protected is connected.

[0003] transformer across the Tr, the main current transformers CT1 for extracting an alternating current for each phase, CT2 is provided, the AC current I _1, which is extracted by these main current transformers CT1, CT2 , I ₂ are introduced into the differential relay 1 and the transformer T
r operates in the event of an internal accident to shut off the circuit breaker CB to protect the transformer Tr.

FIG. 31 is a functional block diagram showing an example of the internal configuration of a conventional differential relay 1. As shown in FIG. Here, the arithmetic processing executed in the central processing unit (CPU) of the digital relay is shown as a functional block diagram. In FIG. 31, a differential relay 1 includes an input transformer 2, an analog / digital converter (hereinafter, referred to as an A / D converter) 3, and a central processing unit (hereinafter, referred to as a CPU) 4.
It consists of

[0005] The input transformer 2 includes main current transformers CT1 and CT2.
Is used to convert the alternating currents I ₁ and I ₂ extracted by the above into appropriate magnitudes. The A / D converter 3 samples the alternating currents I ₁ and I ₂ converted by the input transformer ₂ at regular time intervals (generally, a rated frequency of 50 kHz).
4.8 kHz at a high speed) and converts it into a digital quantity.

Further, the CPU 4 performs digital arithmetic processing using the digital amount converted by the A / D converter 3, and outputs a protection command for the transformer Tr to the circuit breaker CB. That is, the CPU 4 performs the following digital arithmetic processing using the electric quantities I ₁ and I ₂ converted into digital quantities.

Reference numeral 5 denotes a differential protection element (hereinafter simply referred to as a differential element) digitally processed by the CPU 4, and 6 denotes a C element.
The second harmonic detection element (hereinafter, simply referred to as 2f element) digitally processed by the PU 4. First, in the differential element 5, the amplitude value calculation units 11 and 12 extract the fundamental wave component 1f from each of the electric quantities I ₁ and I ₂ to obtain amplitude values | I ₁ | and | I ₂ |.

The scalar sum (hereinafter referred to as suppression current) calculation unit 13 calculates a scalar sum (suppression current = suppression amount) Σ | I | of the amplitude values | I ₁ | and | I ₂ |. On the other hand, the vector sum (hereinafter, referred to as differential current) calculation unit 14 calculates the vector sum (differential current = operation amount) Id of the electric quantities I ₁ and I _2.
Ask for.

Further, the amplitude value calculating section 15 calculates the differential current Id
, A fundamental wave current 1f is extracted from the equation (1), and an amplitude value | Id _1f | is obtained. Further, the differential determination operation unit 16 calculates the suppression current Σ | I
When the relationship between | and the differential current | Id _1f | is equal to or greater than a predetermined value, it is determined that an internal accident has occurred and an output is generated.

On the other hand, in the 2f element 6, the amplitude value calculating section 17 extracts the second harmonic current 2f from the differential current Id to obtain the amplitude value | Id _2f |. When the relationship between the fundamental wave current 1f and the second harmonic current 2f contained in the differential current Id becomes equal to or greater than a predetermined value, the 2f determination calculation unit 18 determines that the current is an inrush current and generates an output. .

On the other hand, the logical product (AN) of the output obtained by inverting the output of the 2f decision operation unit 18 of the 2f element 6 by the NOT operation circuit 19 and the output of the differential decision operation unit 16 of the differential element 5
D) The operation is performed by the AND operation circuit 20, and the output of the AND operation circuit 20 is sent out as the output of the differential relay 1.

In the differential relay 1 having such a configuration, the AC currents I ₁ and I ₂ are converted into digital quantities by the A / D converter 3 through the input transformer 2 and then introduced into the differential element 5. . Electric quantities I ₁ and I ₂ introduced into the differential element 5
Derives the suppression current Σ | I | by the suppression current calculation unit 13 through the amplitude value calculation units 11 and 12, and derives the differential current Id = I ₁ + I ₂ by the differential current calculation unit 14.

As for the differential current Id, 1f is introduced into the amplitude value calculator 15 and the 2f element 6, respectively. In this case, the differential current Id due to the load current and the passing current at the time of an external accident
Becomes zero, and a differential current Id corresponding to the fault current is generated at the time of a fault inside the power transformer Tr.

The amplitude value | Id _1f | of 1f of the differential current Id output from the amplitude value calculation unit 15 and the suppression current Σ | I |
_Are introduced into the differential decision operation unit 16, and | Id _1f | −
When AΣ | I | ≧ B (A and B are constants),
The differential element 5 produces an output upon judging that a transformer internal fault has occurred.
On the other hand, the differential current Id introduced into the 2f element 6 is introduced into the amplitude value calculation unit 17, extracts the second harmonic current 2f from the differential current Id, and outputs the 2f amplitude value | Id _2f | It is introduced into the 2f determination operation unit 18.

The 1f amplitude value | Id _1f | calculated by the differential element 5 is also introduced into the 2f determination calculation unit 18 so as to perform the second adjustment with respect to the fundamental wave current 1f included in the differential current Id. When the degree (| Id _2f | / | Id _1f |) of the wave current 2f becomes equal to or more than a predetermined value, it is determined that the current is an inrush current, and 2f
Element 6 produces the output.

When the 2f element 6 operates, its output is blocked (locked) through the NOT operation circuit 19 by the output of the differential element 5, so that the operation as the differential relay 1 can be prevented. Next, the necessity of countermeasures against the transformer inrush current will be briefly described.

Now, when the circuit breaker CB in FIG. 30 is closed, a voltage is applied to the transformer Tr, and an exciting rush current flows based on the magnetization characteristics of the transformer core. This exciting inrush current apparently flows in from the power system power supply G side and becomes an operation amount (differential current Id) of the differential relay 1 as in an accident inside the transformer Tr. Failure to do so may cause malfunctions (operations that are not accidents).

Therefore, it is necessary to distinguish between the exciting inrush current and the current due to the actual accident. As a method of this, the exciting inrush current contains a large amount of the second harmonic current 2f, and is therefore included in the differential current Id. When the ratio of the second harmonic current 2f to the fundamental wave current If is equal to or larger than a predetermined value (generally, about 15% is often used), the 2f element 6 which is determined to be an inrush current and output is provided, and the differential element 5 The output is locked to prevent the differential relay 1 from malfunctioning.

As described above, in the conventional transformer protection, a differential relay for detecting an accident of a transformer by using a differential current is used, and the differential relay 1 is prevented from malfunctioning due to a transformer inrush current. In addition, a device provided with a 2f element 6 for detecting a second harmonic current included in the exciting inrush current and preventing the relay operation when the content ratio becomes equal to or more than a predetermined value is adopted.

However, in recent years, plans for introducing 1000 kV power transmission and 500 kV long-distance underground cables have been progressing, and as a result, the capacitance of the power system has increased, the resonance frequency has decreased, and the electric current included in the accident current has been reduced. It is expected that the harmonic current near the second harmonic will increase.

As a result, in the conventional differential relay 1 employing the second harmonic current detection method, the 2f element 6 operates even in the event of a fault inside the transformer, and the differential relay 1 malfunctions (excessive). It is impossible to operate even though there is an accident due to the lock).

[0022]

As described above, in the conventional differential relay, the internal fault current includes the harmonic current near the second harmonic in the power system transformer. There has been a problem that it may not be possible to operate reliably in the event of an accident. SUMMARY OF THE INVENTION The present invention has been made to solve the above-described problems, and provides a digital protection relay capable of reliably operating in a transformer inrush current and capable of reliably operating in the event of a transformer internal accident. It is aimed at.

[0023]

An AC current for each phase is introduced across a protected object having a plurality of terminals, and the introduced AC currents are sampled at regular time intervals to obtain an instantaneous value of the AC current. Is converted into a digital quantity, and a differential current for each phase is obtained using the converted digital quantity. When the electrical quantity based on the obtained differential current is equal to or greater than a predetermined value, it is determined that an internal accident has occurred. A digital protection relay comprising a differential protection element having first determining means for generating an output

The digital protective relay according to claim 1 of the present invention, among the determined differential current, digital amount of K instantaneous value of the electrical angle T of intervals _{(i m, i m-1} ,
im ₋₂ , im ₋₃ ,..., _{im− (K−1)} ), and the amplitude value in a constant section of the differential current is calculated by the following amplitude value calculation equation (a). Second determining means for determining whether the obtained amplitude value is equal to or less than a certain value and outputting when the amplitude value is equal to or less than the certain value;
And an exciting inrush current countermeasure element having first return delay means for delaying the output of the second determination means for a predetermined time, and preventing the output of the differential protection element by the output of the exciting inrush current countermeasure element. I did it.

[0025]

(Equation 8)

Next, the operation will be described. The excitation inrush current always has a section where current flows due to magnetic flux saturation of the transformer core during one cycle and a section where current does not flow due to the saturation of the transformer core to be protected (current-free period). On the other hand, the fault current does not have a no-current period due to the superposition of the fundamental current or the unspecified harmonic current.

Note that the current period during which there is no current during one cycle of the inrush current is essentially zero, but the inrush current (= differential current) seen by the protective relay is not necessarily due to the loss of the DC component due to the current transformer. The non-current period is not simply a zero current period, but has a current instantaneous value corresponding to the loss of the DC component of the current transformer, but can be said to be a flat current period in which the change in the current instantaneous value is small. .

Therefore, a small change in the instantaneous current value in a certain section of the current cycle is detected by detecting a small amplitude value of the fundamental wave component in a certain section of the current cycle. When the value is equal to or less than the predetermined value, the change of the instantaneous current value is small, that is, it is determined that the current is an inrush current, and the malfunction of the protection relay due to the inrush current can be prevented.

In order to realize the above, an amplitude value calculation capable of calculating the amplitude value of the fundamental wave component in a certain section of the differential current without being affected by the loss of the DC component of the AC device or the like. An equation is required.
Number of current instantaneous value _{(i m, i m-1} , ..., i mK-1) Basics of the, obtained by applying the least squares method to the equation obtained by curve fitting to a direct current component + fundamental wave component solution Conditional expression of amplitude value of wave component ". This will be described in detail below.

First, the obtained K instantaneous values (i _m ,
im ₋₁ ,..., _imK−1 ) are _subjected to DC component + fundamental wave curve fitting. i _mk = D + Isin (t + Φ−kT) (0) where D: amplitude value of DC, I: amplitude value of fundamental wave component T: sampling interval (arbitrary electrical angle, eg, 15 °) K: sampling number (Natural number, eg, 5) k = 0 to K−1 Φ = (K−1) · T / 2

Here, X = Isin (t), Y = Ico
Assuming that s (t), equation (0) is replaced with equation (0 ′). Further, if the sum of the squares of the curve fitting error is f, f is expressed by equation (1).

[0032]

(Equation 9)

Here, the least squares method is applied. That is, a solution (D, X, Y) that minimizes f in Expression (1) is obtained. The solution that minimizes f is given by the following equations (2), (3),
Since (4) is satisfied, the solution of these three simultaneous equations may be obtained. The process of deriving the solution will be described below.

[0034]

(Equation 10)

First, when the equation (1) is partially differentiated with respect to D,
Equation (5) is obtained. Here, the underlined part in the expression (5) is 0. The basis is proved below.

[0036]

[Equation 11]

[0037]

(Equation 12)

[0038]

(Equation 13) From the formula of the sum of rational examples such as

[0039]

[Equation 14]

[0040]

(Equation 15) Therefore, equation (5) becomes as follows.

[0041]

(Equation 16)

Next, the equation (1) is partially differentiated with respect to X to obtain

[Equation 17]

Further, the equation (1) is partially differentiated with respect to Y,

(Equation 18)

A seventh determining means for determining an amplitude value of the differential current in a certain section, determining whether the obtained amplitude value is equal to or less than a certain value, and outputting when the obtained amplitude value is equal to or less than a certain value; The output of the seventh judging means and the second to sixth judging means
And a first logical sum calculating means for calculating a logical sum with the output of the determining means is newly added to the element for preventing inrush current.

On the other hand, according to a seventh aspect of the present invention, in the digital protection relay according to the first to fifth aspects, the output of the second to sixth determining means is delayed by a predetermined time. The first operation delay means is newly added to the excitation inrush current countermeasure element, and the output of the first operation delay means is used as the input of the first return delay means to the fifth return delay means. In the invention corresponding to claim 8, in the digital protection relay according to any one of claims 1 to 5, equation (8) is obtained from the condition (equation (4)) that minimizes f.

[0046]

[Equation 19]

Since the left side of equation (9) is equal to the left side of equation (10),

(Equation 20)

Solving for X yields equation (11), and solving equation (8) for Y yields equation (12).

(Equation 21)

Here, X = Isin (t), Y = Ico
From the relationship of s (t), the amplitude value I of the fundamental wave component is obtained as follows. In other words, the amplitude value arithmetic expression capable of calculating the amplitude value of the fundamental wave component in a fixed section of the differential current without being affected by the loss of the DC component of the current transformer, etc., is obtained by Expression (A). Can be.

[0050]

(Equation 22)

[0051] Therefore, first, in the digital protection relay of the invention corresponding to claim 1, of the differential current, the digital quantity of the K instantaneous value of the electrical angle T of intervals (i _m, i
_m-1 , im _-2 , im _-3 ,..., _{im- (K-1)} ), and the amplitude value in a constant section of the differential current is calculated by the following amplitude value calculation formula (a). Second determining means for determining whether the obtained amplitude value is equal to or less than a predetermined value and outputting when the amplitude value is equal to or less than the predetermined value, and reset delay means for delaying the output of the second determining means for a predetermined time An exciting inrush current countermeasure element having: an output of the exciting inrush current countermeasure element and an output of the differential protection element are blocked, thereby detecting flatness of the differential current, and detecting an exciting inrush current and an accidental current. Can be surely distinguished.

As a result, even in a transformer of a power system in which the internal fault current includes a harmonic current near the second harmonic, which has been difficult to apply in the past, the inrush current does not operate reliably. In case of an accident inside the transformer, it can operate reliably.

[0053]

(Equation 23)

[0054] digital protection relay according to claim 2 of the present invention, among the determined differential current, digital amount of three instantaneous value of the electrical angle T of intervals _{(i m, i m-1} , i
_m-2 ) is introduced, the amplitude value of the differential current in a certain section is obtained by the following amplitude value calculation equation (b), and it is determined whether or not the obtained amplitude value is equal to or less than the certain value, and the constant value is determined. A third determining means for outputting when the value is equal to or less than a value, and an exciting inrush current countermeasure element having a second return delay means for returning and delaying the output of the third determining means for a predetermined time. The output of the differential protection element is blocked by the output.

[0055]

(Equation 24)

In the digital protection relay according to the second aspect of the present invention, the digital amount (i) of three instantaneous values of the differential current at intervals of the electrical angle T degrees (for example, 15 electrical degrees at 1200 Hz sampling) among the differential currents. _m , im _-1 , im _-2 )
Introducing, "three current instantaneous value _{(i m, i m-1} ,
i _m-2 ) is a conditional expression for the amplitude value of the fundamental wave component in the solution obtained by applying the least squares method to the equation obtained by curve fitting the DC component + the fundamental wave component. By substituting K = 3, an amplitude value in a constant section of the differential current is obtained by an amplitude value calculation equation (b) obtained as follows, and it is determined whether the obtained amplitude value is equal to or less than a certain value. An excitation inrush current countermeasure element having third determination means for determining and outputting when the value is equal to or less than a predetermined value, and return delay means for delaying the output of the third determination means for a predetermined time. By blocking the output of the differential protection element, the flatness of the differential current can be detected, and the inrush current and the fault current can be reliably distinguished.

Next, the derivation of the amplitude value calculation equation (b) will be described. Substituting K = 3 into equation (a),

(Equation 25)

[0058]

(Equation 26)

[0059] Digital coercive relay according to claim 3 of the present invention, among the determined differential current, digital amount of four instantaneous value of the electrical angle T of intervals _{(i m, i m-1} , i _m-2 ,
i _m-3 ), the amplitude value of the differential current in a certain section is obtained by the following amplitude value calculation formula (c), and it is determined whether the obtained amplitude value is equal to or less than the certain value. An excitation inrush current countermeasure element having a fourth determination means for outputting when the value is equal to or less than a predetermined value, and a third return delay means for returning and delaying the output of the fourth determination means for a predetermined time; , The output of the differential protection element is blocked.

[0060]

[Equation 27]

In the digital protection relay according to the third aspect of the present invention, the digital amount (i) of four instantaneous values of the differential current at intervals of electrical angle T degrees (for example, electrical angle 15 degrees at 1200 Hz sampling) out of the differential currents. _m , im _-1 , im _-2 ,
i _m−3 ), and “four current instantaneous values (i _m ,
i _m−1 , im ₋₂ , i _m−3 ) is obtained by applying the least-squares method to an equation obtained by curve-fitting a DC component + a fundamental component to the amplitude value of the fundamental component. The amplitude value in a constant section of the differential current is obtained by an amplitude value calculation expression (c) obtained as follows by substituting K = 4 into the conditional expression (b), and the obtained amplitude Exciting inrush current countermeasure element having fourth determining means for determining whether the value is equal to or less than a predetermined value and outputting when the value is equal to or less than the predetermined value, and return delay means for delaying the output of the fourth determining means for a predetermined time. By detecting the flatness of the differential current by blocking the output of the differential protection element by the output of the excitation inrush current countermeasure element, it is possible to reliably distinguish the excitation inrush current from the fault current. It becomes possible.

As a result, even in a transformer of a power system in which the internal fault current includes a harmonic current near the second harmonic, which has been difficult to apply in the past, the inrush current does not operate reliably. In case of an accident inside the transformer, it can operate reliably.

Next, the derivation of the amplitude value calculation formula (C) will be described. Substituting K = 4 into equation (a),

[Equation 28]

[0064]

(Equation 29)

[0065] Digital coercive relay according to claim 4 of the present invention, among the determined differential current, digital amount of five instantaneous value of the electrical angle T of intervals _{(i m, i m-1} , i _m-2 ,
im _-3 , im _-4 ), and the amplitude value of the differential current in a certain section is obtained by the following amplitude value calculation formula (d). Whether the obtained amplitude value is equal to or less than the certain value is determined. A fifth judging means for judging whether the value is equal to or less than a predetermined value, and an exciting rush current countermeasure element having a fourth resetting delaying means for delaying the output of the fifth determining means for a predetermined time. The output of the differential protection element is blocked by the output of the excitation inrush current suppression element.

[0066]

[Equation 30]

According to the digital protection relay of the invention corresponding to claim 4, in the differential current, the digital quantity (i) of five instantaneous values at intervals of electrical angle T degrees (for example, electrical angle 15 degrees at 1200 Hz sampling) among differential currents. _m , im _-1 , im _-2 ,
introducing a _{i m-3, i m-} 4), "five current instantaneous value _{(i m, i m-1} , i m-2, i m-3, i m-4), the DC component + A conditional expression for the amplitude value of the fundamental wave component in the solution obtained by applying the least squares method to the equation fitted with the curve of the fundamental wave component. In the amplitude value calculation formula (d) obtained in the step (d), the amplitude value of the differential current in a certain section is determined, and it is determined whether or not the obtained amplitude value is a certain value or less. 5
Determination means, and an excitation inrush current countermeasure element having a return delay means for delaying the output of the fifth determination means for return for a predetermined time, and the output of the excitation inrush current countermeasure element includes:
By blocking the output of the differential protection element, it is possible to detect the flatness of the differential current and to reliably distinguish the exciting inrush current from the fault current.

As a result, even in a transformer of a power system in which the internal fault current includes a harmonic current near the second harmonic, which has been difficult to apply in the past, the inrush current does not operate reliably. In case of an accident inside the transformer, it can operate reliably.

Next, the derivation of the amplitude value calculation formula (d) will be described. Substituting K = 5 into equation (a),

(Equation 31)

[0070]

(Equation 32)

[0071] Digital coercive relay according to claim 5 of the present invention, among the determined differential current, digital amount of six instantaneous value of the electrical angle T of intervals _{(i m, i m-1} , i _m-2 ,
im _-3 , im _-4 , im _-5 ), and the amplitude value in a constant section of the differential current is calculated by the following amplitude value calculation formula (e). A sixth determining means for determining whether the value is equal to or less than a predetermined value and outputting the result when the value is equal to or less than the predetermined value, and a fifth means for delaying the output of the sixth determining means for a predetermined time.
An inrush current suppression element having a return delay means of
The output of the differential protection element is blocked by the output of the excitation inrush current suppression element.

[0072]

[Equation 33]

According to the digital protection relay of the present invention, six instantaneous digital values (i) of the differential current at intervals of an electrical angle of T degrees (for example, 15 degrees in 1200 Hz sampling) are used. _m , im _-1 , im _-2 ,
_{i m-3, i m-} 4, i m-5) was introduced into the "six current instantaneous value _{(i m, i m-1} , i m-2, i m-3, i m-4, im _-5 )
Is a conditional expression for the amplitude value of the fundamental wave component in the solution obtained by applying the least squares method to the expression obtained by curve-fitting the DC component + the fundamental wave component. That is, K = 6 is substituted into the equation (a). Then, an amplitude value in a certain section of the differential current is obtained by an amplitude value calculation equation (e) obtained as described below, and it is determined whether or not the obtained amplitude value is a certain value or less. And a return delay means for delaying the output of the sixth determination means for a predetermined time by returning the excitation inrush current countermeasure element. By blocking the output of the dynamic protection element, the flatness of the differential current can be detected and the inrush current and the fault current can be reliably distinguished.

As a result, even in a transformer of a power system in which the internal fault current includes a harmonic current near the second harmonic, which has been difficult to apply in the past, the inrush current does not reliably operate. In case of an accident inside the transformer, it can operate reliably.

Next, the derivation of the amplitude value calculation equation (e) will be described. Substituting K = 6 into equation (a),

(Equation 34)

[0076]

(Equation 35)

According to a sixth aspect of the present invention, there is provided a digital relay device according to the sixth aspect of the present invention, wherein, of the obtained differential currents, the same or the same as the number K at intervals of electrical angle T 'degrees which is the same as or different from the electrical angle T. 'digital amount of pieces of the instantaneous value (i _m' different _{K, i m-1 ',} i m-2', i m-3 ', ..., i
_{m- (K'-1)} ') and calculate the amplitude value of the differential current in a certain section by the following amplitude value calculation formula (f), and determine whether the obtained amplitude value is equal to or less than a certain value. A seventh determining means for determining whether the output is equal to or less than a predetermined value, and a fourth calculating means for calculating a logical sum of an output of the seventh determining means and an output of the second to sixth determining means. The logical OR operation means 1 is newly added to the element for suppressing the inrush current.

[0078]

[Equation 36]

Usually, the excitation inrush current is generated when a voltage is applied to the transformer, but the excitation inrush current is also generated by the voltage rise when the fault outside the protection range is eliminated (= at the time of recovery from the fault). May be. At this time, unlike the case where a normal transformer voltage is applied, a current passing through the transformer is generated in addition to the inrush current. In such a case, the non-current period of the exciting inrush current (= differential current) seen by the protection relay is the current period affected by the current passing through the transformer due to the configuration affected by the tap position of the transformer. Becomes

In general, the magnitude of the exciting rush current generated at the time of recovery from an accident is smaller than that of the exciting rush current generated when a normal transformer voltage is applied, and the non-current period is generated when the normal transformer voltage is applied. Is longer than the non-current period of the exciting inrush current. On the other hand, the amplitude value calculation expressions according to claims 1 to 5 have a feature that the influence of the higher harmonics is reduced as the calculation interval is wider. Reduce the effect of the current passing through the transformer,
It is possible to more reliably detect the non-current period of the inrush current at the time of recovery from the accident, and it is possible to prevent malfunction of the protection relay due to the inrush current.

Therefore, first, in the digital protection relay according to the present invention corresponding to claim 6, in the digital protection relay according to claim 1, of the obtained differential currents, an electrical angle T 'degree interval is used. 'digital amount of pieces of the instantaneous value (i _m' of _{K, i m-1 ',} i m-2', i m-3 ', ...,
i _{m− (K′−1)} ′), and into the amplitude value calculation formula (f),

[0082]

(37)

Then, the amplitude value of the differential current in a constant section is determined in a wide calculation section, and it is determined whether or not the determined amplitude value is equal to or smaller than a predetermined value, and output when the obtained amplitude value is equal to or smaller than the predetermined value. And the seventh judging means more reliably detects the flatness of the inrush current at the time of recovery from the accident, and further compares the output of the seventh judging means with the output of the second judging means. By adding the first logical sum calculating means for calculating the logical sum to the element for preventing the inrush current, the inrush current and the fault current can be distinguished more reliably.

As a result, even in a transformer of a power system in which the internal fault current includes a harmonic current near the second harmonic, which has been difficult to apply in the past, the inrush current does not operate reliably. In case of an accident inside the transformer, it can operate reliably.

A digital relay according to a seventh aspect of the present invention is the digital protective relay according to any one of the first to fifth aspects, wherein the outputs of the second to sixth determining means are delayed for a predetermined time. The first operation delay means is newly added to the excitation inrush current countermeasure element, and the output of the first operation delay means is used as the input of the first return delay means to the fifth return delay means.

According to the digital protection relay of the invention corresponding to claim 7, in the digital protection relay according to any one of claims 1 to 5, the second determining means to the sixth
The first operation delay means for delaying the operation of the output of the determination means for a predetermined time is added to the excitation inrush current countermeasure element,
Even if accidental currents have a short-term flat part accidentally, there is no unnecessary output of the inrush current countermeasure element, and the protective relay can operate normally, so that the inrush current and the inrush current can be more reliably distinguished. Becomes possible.

As a result, even in a transformer of a power system in which the internal fault current includes a harmonic current near the second harmonic, which has been difficult to apply in the past, the inrush current does not operate reliably. In case of an accident inside the transformer, it can operate reliably.

The digital protection relay according to claim 8 of the present invention is the digital protection relay according to any one of claims 1 to 5, wherein the current output of the second determination means to the sixth determination means and the second A first AND operation unit for performing an AND operation with the output of one or more cycles before the judgment unit to the sixth judgment unit is newly added, and the output of the first AND operation unit is added to the first AND operation unit. 1st return delay means to 5th
Input of the return delay means.

According to the digital protection relay of the invention corresponding to claim 8, in the digital protection relay according to any one of claims 1 to 5, the second determination means to the sixth
A first AND operation means for calculating an AND operation between the output of the judgment means and the output of one or more cycles before the second to sixth judgment means is newly added, and the AND operation is performed. The output of the first return delay means to the fifth return delay means.
Even if the fault current transiently has a short-term flat part, there is no unnecessary output of the inrush current countermeasure element, and the protection relay can operate normally, Inrush current and fault current can be distinguished more reliably.

As a result, even in a transformer of a power system in which the internal fault current includes a harmonic current near the second harmonic, which has been difficult to apply in the past, the inrush current does not operate reliably. In case of an accident inside the transformer, it can operate reliably.

A digital relay according to a ninth aspect of the present invention is the digital type protective relay according to any one of the first to fifth aspects, wherein the current value of the determined amplitude value is 1
Compare the value before the cycle or multiple cycles or the value before one sampling to find the larger value,
An eighth determining means for determining whether the larger value is equal to or less than a certain value and generating an output when the value is equal to or less than the certain value is newly added, and outputting the output of the eighth determining means to the first return. The input is made to the delay means to the fifth return delay means.

According to a ninth aspect of the present invention, there is provided a digital protection relay according to any one of the first to fifth aspects, wherein the current value of the obtained amplitude value is one cycle or a plurality of cycles. Eighth determination means for comparing the previous value with the previous value to determine any larger value and determining whether the larger value is equal to or less than a certain value and generating an output when the value is equal to or less than the certain value is newly provided. And the output of the eighth judging means is connected to the first return delay means to the fifth
Even if the fault current transiently has a short-term flat portion, there is no unnecessary output of the inrush current countermeasure element, and the protective relay can operate normally, Inrush current and fault current can be distinguished more reliably.

As a result, even in a transformer of a power system in which the internal fault current includes a harmonic current near the second harmonic, which has been difficult to apply in the past, the inrush current does not reliably operate. In case of an accident inside the transformer, it can operate reliably.

According to a tenth aspect of the present invention, there is provided the digital protection relay according to the first to ninth aspects, wherein any one of the terminals to be protected having a plurality of terminals or each of the plurality of terminals is provided. The AC voltage for each phase is introduced, and the introduced AC voltage is sampled at fixed time intervals, and is converted into a digital value of an instantaneous value of the AC voltage, and the converted digital value is used for each phase. A ninth determining means for determining an amplitude value of the voltage and generating an output when the determined amplitude value of the voltage is equal to or more than a predetermined value; an output of the ninth determining means and the second return delay means or The second AND operation means for calculating the AND operation with the output of the fifth return delay means is newly added to the element for preventing the inrush current.

Further, when attention is paid to the terminal voltage of the transformer,
The terminal voltage of the transformer is large when applying a voltage that generates inrush current, and the terminal voltage is small when an accident occurs inside the transformer.
There is a difference. Therefore, by using the means for determining the magnitude of the amplitude value of the voltage together, it is possible to more reliably discriminate the excitation inrush current and the internal fault current,
It is possible to prevent a malfunction of the protection relay due to the inrush current.

Therefore, first, in a digital protection relay according to the present invention corresponding to claim 10, in the digital protection relay according to any one of claims 1 to 9, any one of the objects to be protected having a plurality of terminals is provided. The AC voltage for each phase of one terminal is introduced, the introduced AC voltage is sampled at fixed time intervals, and is converted into a digital value of an instantaneous value of the AC voltage. Ninth determining means for determining an amplitude value of a voltage for each phase and generating an output when the determined amplitude value of the voltage is equal to or more than a predetermined value; and an output of the ninth determining means and the second return. A second logical product calculating means for calculating a logical product with the output of the delay means to the fifth return delay means is newly added to the excitation inrush current countermeasure element, and the magnitude of the voltage is detected. Excitation inrush current It is possible to more reliably distinguish the fault current.

As a result, even in a transformer of a power system in which the internal fault current includes a harmonic current near the second harmonic, which has been difficult to apply in the past, the inrush current does not operate reliably. In case of an accident inside the transformer, it can operate reliably.

According to a eleventh aspect of the present invention, there is provided the digital protection relay according to the first to ninth aspects, wherein any one of the terminals to be protected having a plurality of terminals or each of the plurality of terminals is provided. The AC voltage for each phase is introduced, and the introduced AC voltage is sampled at a constant time interval and converted into a digital quantity of an instantaneous value of the AC voltage. K
Digital values of the instantaneous values ( _Vm , _Vm-1 , _Vm-2 , Vm
_m-3 , ..., _{Vm- (K-1)} ), and the amplitude value in a constant section of the AC voltage is calculated by the following amplitude value calculation formula (g). A tenth judging means for judging whether or not the value is equal to or more than a certain value and outputting when the value is equal to or more than the certain value; and an output of the tenth judging means and an output of the second to eighth judging means. A third logical product calculating means for calculating a logical product is newly added to the excitation rush current countermeasure element.

[0099]

(38)

Further, when attention is paid to the terminal voltage of the transformer for a short period, the terminal voltage at the time of applying a voltage at which an exciting rush current is generated is large, and the terminal voltage at the time of an accident inside the transformer is small. In addition, during the period of no inrush current, no current flows, so no voltage drop occurs, and the largest voltage amplitude value is obtained. Is characterized by a remarkable appearance.

Therefore, the magnitude of the amplitude value of the voltage is obtained in the same calculation period as the calculation of the amplitude value of the differential current, and means for judging whether or not the obtained amplitude value is a certain value or more is also used. Thus, it is possible to more reliably discriminate between the inrush current and the internal fault current, and it is possible to prevent a malfunction of the protection relay due to the inrush current.

According to the digital protection relay of the present invention corresponding to claim 11, in the digital protection relay according to any one of claims 1 to 9, any one of the terminals to be protected having a plurality of terminals or a plurality of terminals. The AC voltage of each phase is introduced, and the introduced AC voltage is sampled at fixed time intervals and converted into a digital value of an instantaneous value of the AC voltage. A digital quantity of K instantaneous values (V _m ,
V _m−1 , V _m−2 , V _m−3 ,..., V _{m− (K−1)} )
The following amplitude value calculation formula (g),

[0103]

[Equation 39]

A tenth determination means for determining an amplitude value of the AC voltage in a certain section, determining whether the obtained amplitude value is a certain value or more, and outputting when the amplitude value is a certain value or more; and A third logical product calculating means for calculating a logical product of the output of the tenth determining means and the outputs of the second to eighth determining means is newly added to the excitation inrush current countermeasure element. Then, by detecting the amplitude value of the voltage in the same short calculation period as the differential current, it becomes possible to further distinguish the inrush current and the fault current.

As a result, even in a transformer of an electric power system in which the internal fault current includes a harmonic current near the second harmonic, which has been difficult to apply in the past, the inrush current does not operate reliably. In case of an accident inside the transformer, it can operate reliably.

Further, when attention is paid to the change in the terminal voltage of the transformer, the terminal voltage of the transformer at the time of voltage application such that an exciting rush current is generated is greatly increased as compared with before the voltage application. There is a difference that the terminal voltage decreases or hardly increases.

Therefore, by using the means for judging the increase in the amplitude value of the voltage together, it is possible to more reliably discriminate between the inrush current and the internal fault current, and the protection relay by the inrush current is used. Can be prevented from malfunctioning.

A digital protection relay according to a twelfth aspect of the present invention is the digital protection relay according to the first to eleventh aspects, wherein any one of the plurality of terminals or one of the plurality of terminals to be protected has a plurality of terminals. The AC voltage for each phase is introduced, the introduced AC voltage is sampled at fixed time intervals, and converted into a digital quantity of an instantaneous value of the AC voltage, and the voltage for each phase is converted using the converted digital quantity. An eleventh determination means for generating an output when the amplitude value of the determined voltage increases by a predetermined value or more, and a sixth recovery means for delaying the output of the eleventh determination means for a predetermined time. A delay means and a fourth AND operation means for calculating an AND of the output of the sixth return delay means and the exciting rush current countermeasure element are newly added, and the fourth AND operation means is provided. To output Ri, and so as to prevent the output of the differential protection element.

As a result, even in a transformer of a power system in which the internal fault current includes a harmonic current near the second harmonic, which has been difficult to apply in the past, the inrush current certainly becomes inoperable. In case of an accident inside the transformer, it can operate reliably.

According to a thirteenth aspect of the present invention, in the digital protection relay according to the first to twelfth aspects, the second operation delay means for operating the output of the differential protection element for a predetermined time. And a fifth logical product calculating means for calculating a logical product of the output of the differential protection element and the output of the exciting rush current countermeasure element, and the output of the fifth logical product calculating means The output of the second operation delay means is blocked.

As a result, even in a transformer of an electric power system in which the internal fault current includes a harmonic current near the second harmonic, which has been difficult to apply in the past, the inrush current does not operate reliably. In case of an accident inside the transformer, it can operate reliably.

FIG. 1 is a functional block diagram showing an example of the construction of a differential relay for protecting a transformer, which is a digital protection relay according to the present invention. In FIG. 1, the same parts as those in FIG. The description thereof is omitted, and only different portions will be described here.

That is, the differential relay 1 of this embodiment is
As shown in FIG. 1, the exciting inrush current countermeasure element 6 in FIG. 31 is omitted, and a new exciting inrush current countermeasure element 61 is provided instead.

The excitation inrush current countermeasure element 61 comprises an amplitude value calculation unit 21, a flatness determination calculation unit 22, and a return delay timer 23. Here, the amplitude value calculation unit 21
Is to calculate an amplitude value in a certain section of the waveform of the differential current Id obtained by the differential current calculation section 14 of the differential element 5.

[0115] That is, in this example, of the differential current, the digital quantity of the K instantaneous value of the electrical angle T of intervals (i _m, i
_{m-1, i m-2} , i m-3, ..., introduced _{i m- (K-1))} , which obtains an amplitude value at a constant interval of the differential current by the amplitude value calculation formula (A) It is.

[0116]

(Equation 40)

Further, the flatness determination calculating section 22 determines whether or not the amplitude value obtained by the amplitude value calculating section 21 is equal to or less than a certain value. Is what happens. Further, a return delay timer 2
Reference numeral 3 denotes a signal which has a delay time of about one cycle or more and makes the output of the flatness determination operation unit 22 continuous. Thus, the output of the differential element 5 is blocked by the output of the return delay timer 23.

Next, the operation of the differential relay 1 according to the present embodiment configured as described above will be described. Since the operation of the differential element 5 is the same as that of the case of 31,
Here, the description is omitted. In FIG. 1, the differential current Id derived by the differential current calculator 14 of the differential element 5 is:
Introduced to the excitation inrush current countermeasure element 61, the amplitude calculation unit 21
The calculation for detecting the amplitude value is performed in the step, and the amplitude value J is obtained. Then, when the amplitude value J obtained here is equal to or smaller than the predetermined value k, the flatness determination calculation unit 22 generates an output.

On the other hand, the output of the return delay timer 23 is set to NO.
Inverted by the T operation circuit 19, the logical product operation circuit 2
By performing a logical product operation with the output of the differential element 5 at 0, the output of the differential element 5 operating by the inrush current can be prevented, and malfunction as the differential relay 1 can be prevented.

Hereinafter, this point will be described more specifically. First, the difference between the characteristics of the current waveform of the fault current due to the fault inside the transformer and the current waveform of the exciting inrush current will be described. FIG.
It is a waveform diagram which shows the difference of the characteristic of the current waveform of fault current (a) and excitation inrush current (b). In the excitation inrush current, the section where the transformer core is saturated during one cycle and current does not flow ( A current-free period always exists, whereas the fault current does not have a current-free period due to the superposition of a fundamental current or an unspecified harmonic current.

Note that the current inactive period existing in one cycle of the inrush current is essentially zero, but the inrush current (= differential current) seen by the protection relay is not necessarily due to the loss of DC component by the current transformer CT. It can be said that the non-current period of Id) is not a simple current zero, but a flat current period with little change in instantaneous value.

Therefore, by looking at the fact that the amplitude value in a certain section in one cycle of the current is small, that is, by observing the flatness, it can be determined that the current is an inrush current, and malfunction of the differential relay 1 is prevented. That is, the following calculation for obtaining the amplitude value is performed in the amplitude value calculation unit 21 of the excitation inrush current countermeasure element 61.

FIG. 3 (a) shows a value when the exciting inrush current is converted into a digital value of its instantaneous value. In FIG. 3 (a), the instantaneous value of the current i _m, 1 sampling (hereinafter referred to as sp) i _m-1 the instantaneous value of the front,
The instantaneous value before ₂ sp is set as im _-2 , the instantaneous value before ₃ sp is set as im _-3 , ..., the instantaneous value before (K-1) sp is set as im- _(k-1) .

[0124] To explain the amplitude value calculated at the instantaneous values of FIG. 3 (a), K pieces of the instantaneous values of the given section in one cycle (e.g., the section _{a i m ~i m - (k} -1)) from Is determined by the following equation (a). The fixed section may be any section that is smaller than the no-current period at the maximum exciting inrush current, and is not particularly limited.

This value of J is referred to as an amplitude value, and is 1
It represents an amplitude value in a certain section in a cycle, and the amplitude value J becomes zero only when the current waveform in the certain section in one cycle of the differential current is flat.

[0126]

[Equation 41]

As in the case of the amplitude value J in the section a, calculation is performed using the past K sp numbers for each sp (in FIG. 3A, the sections b and c are used).
..), It is possible to always see the amplitude value in a certain section, and to determine the individual amplitude values Ja, Jb, Jc... As shown in the calculation result in the amplitude value calculation unit 21 in FIG. Become.

The value of the amplitude value J at the differential current Id due to the exciting inrush current having a flat section as shown in FIG. 3B is obtained when the entire calculation section is included in the flat portion of the differential current Id ( In the section a) of FIG. 3A, the value becomes the minimum. Further, when the amplitude value J takes a value smaller than the constant value k, the flatness determination calculation unit 22 generates an output like the calculation result of the flatness determination calculation unit 22 in FIG.

The constant value k is a value for discriminating the fault current from the flat portion of the exciting rush current, and does not cause an erroneous determination due to a loss of the DC component due to the current transformer CT or a calculation error of the relay. Value.

Next, an example of detecting flatness between the fault current and the inrush current will be described with reference to FIG. First, the inrush current (b) will be described. As described above, the amplitude value calculation unit 21 of the differential relay always calculates the amplitude value J of a certain section (here, has a calculation section of t1) for each sp, and the excitation inrush current having a flat section. The value of the amplitude value J at the differential current Id becomes minimum when the entire calculation section (t1) is included in the flat portion, and the value becomes a constant value k
The flatness determination calculation unit 22 generates an output in the following cases.

[0131] t1 in FIG. 4 shows a calculation section when all the points are included in the flat portion. Thereafter, the flatness in the calculation section disappears with the rise of the current, and the amplitude value J
During a time t2 until is equal to or more than the constant value k, the flatness determination calculation unit 22 generates an output. In addition, since the same detection is performed in the next cycle, the flatness determination calculation unit 22 always generates an output once in one cycle.

For this reason, the output of the flatness determination operation section 22 is
Since the output is intermittent every one cycle, continuation is performed by the return delay timer 23 having a time of about one cycle or more, and the output of this return delay timer is used as the output of the excitation inrush current countermeasure element 61. The output of the return delay timer 23 is inverted by the NOT operation circuit 19, and the AND operation with the output of the differential element 5 is performed by the AND operation circuit 20, so that the operation is performed by the inrush current. The output of the differential element 5 can be blocked, and malfunction as the differential relay 1 can be prevented.

On the other hand, the fault current (a) may include a large amount of harmonic currents in addition to the fundamental current, and particularly, the fault current (a) near the second harmonic at which the conventional differential relay malfunctions. Even for the harmonics, a flat section only for the time t1 does not occur, so that there is no output of the flatness determination operation unit 22 and the output of the differential determination operation unit 16 passes through the logical product operation circuit 20 to the differential relay 1 as it is. It becomes an output and normal operation can be performed.

In the above description, the value representing the flatness has been described based on the amplitude value J, but may be a value represented by the following general formula (formula (a-1)). That is, of the calculated differential currents, K of electrical angle T degree intervals
Digital amount of pieces of the instantaneous value _{(i m, i m-1} , i m-2,
.., _{Im- (K-1)} ), and a value obtained by raising the amplitude value in a certain section to the Nth power is obtained.

That is, the N of the amplitude value represented by the equation (a-1)
The power J ^N is obtained as an amplitude value calculation. Then, the excitation inrush current countermeasure element 6 including the flatness determination calculation unit 22 that generates an output when the N-th power J ^N of the obtained amplitude value is equal to or smaller than the constant value k.
1 and the output thereof blocks the output of the differential element 5, whereby the same operation as in the case described above can be achieved.

[0136]

(Equation 42)

For example, when N = 2, (A-1)
The equation (a-2) may be used instead of the equation.

[Equation 43]

As described above, in the present embodiment, the difference between the waveforms of the transformer inrush current and the transformer internal fault current, that is, the excitation inrush current is caused by the saturation of the magnetic flux of the transformer core during one cycle. While there is always a flat section where the current flows and the saturation of the transformer core is released and the current does not flow, the fault current has a flat section in the fixed section due to the fundamental current or the superposition of an unspecified number of harmonic currents. It is noted that it does not occur.

[0139] Then among the differential current Id, a digital quantity of the K instantaneous value of the electrical angle T of intervals _{(i m, i m-1} ,
i _m-2, ..., introduced _{i m- (K-1))} , determine the values of the amplitude value raised to the power N of the constant interval, inrush when th power N of the amplitude value is less than a predetermined value An excitation rush current countermeasure element 61 which determines an electric current and generates an output is provided to detect the flatness of the differential current Id, and the output of the differential element 5 is prevented by the output of the excitation rush current countermeasure element 61. did.

Therefore, the inrush current and the fault current can be reliably distinguished from each other, and it has been difficult to apply the prior art. Even in the transformer Tr of the power system in which the internal fault current includes the harmonic current near the second harmonic, the transformer inrush current surely becomes inoperable, and operates reliably in the event of a transformer internal fault. A digital protection relay capable of performing the above-described operations can be obtained.

FIG. 5 is a functional block diagram showing a configuration example of a differential relay for protecting a transformer, which is a digital protection relay according to the second embodiment. The same parts as those in FIG. The description is omitted, and only different portions will be described here. The configuration of the differential element 5 is shown in FIG.
5 is partially omitted from FIG.

That is, as shown in FIG. 5, the differential relay 1 of the present embodiment has the
1 is omitted, and instead, a new exciting inrush current countermeasure element 62 is provided. The excitation inrush current countermeasure element 62 includes an amplitude value calculator 24 and a flatness determination calculator 22.
And a return delay timer 23.

Here, the amplitude value calculator 24 calculates the differential current I obtained by the differential current calculator 14 of the differential element 5.
The amplitude value in a certain section of the waveform d is obtained. That is, in this example, of the differential current, the digital quantity of three instantaneous value of the electrical angle T of intervals _{(i m, i m-1} , i m-2)
And the amplitude value of the differential current in a certain section is obtained by the following amplitude value calculation formula (b).

[0144]

[Equation 44]

Further, the flatness determination calculating section 22 determines whether or not the amplitude value obtained by the amplitude value calculating section 24 is equal to or less than a certain value. Is what happens. That is, in the present example, it is determined whether or not the amplitude value obtained by the amplitude value calculation unit 24 is equal to or less than a certain value.

Further, the return delay timer 23 has a delay time of about one cycle or more, and is used to make the output of the flatness determination operation unit 22 continuous. Thereby, the output of the differential element 5 can be blocked by the output of the return delay timer 23.

Next, the operation of the differential relay 1 according to the present embodiment will be described. The operation of the differential element 5 is the same as that in the case of FIG. 31, and the description thereof is omitted here. In FIG. 5, the differential current Id derived by the differential current calculator 14 of the differential element 5 is introduced into the exciting rush current countermeasure element 62, and is calculated by the amplitude value calculator 24 to detect flatness. To obtain the amplitude value J.
Then, when the amplitude value J obtained here is equal to or smaller than the predetermined value k, the flatness determination calculation unit 22 generates an output.

On the other hand, the output of the return delay timer 23 is set to NO.
Inverted by the T operation circuit 19, the logical product operation circuit 2
By performing a logical product operation with the output of the differential element 5 at 0, the output of the differential element 5 operating by the inrush current can be prevented, and malfunction as the differential relay 1 can be prevented.

Hereinafter, this point will be described more specifically. The difference between the characteristics of the current waveform of the fault current caused by the fault inside the transformer and the current waveform of the exciting inrush current is exactly the same as in the case of the first embodiment, and the description thereof is omitted. Also in the present embodiment, similarly to the case of the first embodiment, it is determined that the excitation rush current is due to the fact that the amplitude value in a certain section in one cycle of the current is small, that is, the flatness is observed. To prevent the differential relay 1 from malfunctioning. That is, the amplitude value calculation unit 24 of the excitation inrush current countermeasure element 62 performs the following calculation for obtaining the amplitude value.

FIG. 6A shows a value when the exciting inrush current is converted into a digital value of the instantaneous value. In FIG. 6 (a), the instantaneous value of the current i _m, 1 sampling (hereinafter referred to as sp) i _m-1 the instantaneous value of the front,
The instantaneous value ₂ sp before is set as im _-2 .

[0151] To explain the amplitude value calculated at the instantaneous values of FIG. 6 (a), 3 pieces of the instantaneous values of the given section in one cycle (e.g., i _m ~i _m-2 sections a), the amplitude of the following It is determined by the value calculation formula (b).

[0152]

[Equation 45]

The fixed section may be any section that is shorter than the no-current period at the maximum inrush current, and is not particularly limited. This value of J is referred to as an amplitude value and represents an amplitude value in a certain section in one cycle of the differential current. Only when the current waveform in the certain section in one cycle of the differential current is flat, The amplitude value J becomes zero.

As in the case of the amplitude value J in the section a, calculation is performed using the past three sp numbers for each sp (in FIG. 6A, the sections b and c are used).
..), It is possible to always see the amplitude value in a certain section, and to determine the individual amplitude values Ja, Jb, Jc... As shown in the calculation result in the amplitude value calculation unit 24 in FIG. Become.

The value of the amplitude value J at the differential current Id due to the exciting rush current having a flat section as shown in FIG. 6B is obtained when the entire calculation section is included in the flat portion of the differential current Id ( In the section a) of FIG. 6A, the value becomes the minimum. Further, when the amplitude value J takes a value smaller than the fixed value k, the flatness determination calculation unit 22 generates an output like the calculation result of the flatness determination calculation unit 22 in FIG.

The constant value k is a value for discriminating the fault current from the flat portion of the inrush current, and does not cause erroneous determination due to a loss of DC component due to the current transformer CT or a calculation error of the relay. Value. In the above description, the value representing the flatness has been described based on the amplitude value J, but may be a value represented by the following general formula (formula (b-1)).

That is, of the calculated differential currents,
Digital amount of three instantaneous value of the electrical angle T of intervals (i _m,
i _m−1 , i _m−2 ) are introduced, and a value obtained by raising the amplitude value in a certain section to the Nth power is obtained. That is, obtaining the N-th power J ^N amplitude values represented by the (b -1) where the amplitude value calculation.

[0158]

[Equation 46]

For example, when N = 2, (b-1)
The equation (b-2) may be used instead of the equation.

[Equation 47]

Then, the N-th power J ^N of the obtained amplitude value is obtained.
Flatness calculating unit 22 that produces an output when is less than or equal to a constant value k
By providing an exciting inrush current countermeasure element 62 having the following, the output of which blocks the output of the differential element 5,
The same operation as in the case described above is achieved.

In the present embodiment, three s
Since the calculation is performed using the p number, in the case of a protective relay having a sp interval of T, the calculation interval is 3T. In this case, when the entire calculation section 3T is included in the flat portion of the differential current Id, the value of the amplitude value J becomes minimum. According to the present embodiment, when applied to a transformer in which the flat portion of the maximum inrush current is 3T or more, it is easy to distinguish between the fault current and the flat portion of the inrush current.

In the present embodiment, the digital amount (i) of three instantaneous values of the differential current Id at an electrical angle T-degree interval is used.
_m , im _-1 and im _-2 ) are introduced to obtain a value obtained by multiplying the amplitude value in a certain section to the Nth power. Since the flatness of the differential current Id is detected by detecting the flatness of the differential current Id, the output of the differential element 5 is blocked by the output of the exciting rush current countermeasure element 62. The inrush current and the fault current can be reliably distinguished from each other, and it has been difficult to apply the conventional technology described above.

Even in the transformer Tr of the power system in which the internal fault current includes the harmonic current near the second harmonic, the inrush current of the transformer extinguishes reliably, and operates reliably in the event of a fault inside the transformer. And a digital protection relay capable of performing such operations.

FIG. 7 is a functional block diagram showing an example of the configuration of a differential relay for protecting a transformer, which is a digital protection relay according to the third aspect. The same parts as those in FIG. The description is omitted, and only different portions will be described here. The configuration of the differential element 5 is shown in FIG.
Therefore, FIG. 7 omits a part of the configuration.

That is, as shown in FIG. 7, the differential relay 1 of the present embodiment has the
1 is omitted, and in place of this, a new exciting inrush current countermeasure element 63 is provided. The excitation inrush current countermeasure element 63 includes an amplitude value calculator 25 and a flatness determination calculator 22.
And a return delay timer 23.

Here, the amplitude value calculator 25 calculates the differential current I obtained by the differential current calculator 14 of the differential element 5.
The amplitude value in a certain section of the waveform d is obtained. That is, in this example, of the differential current, the digital quantity of four instantaneous value of the electrical angle T of intervals _{(i m, i m-1} , i m-2,
im ₋₃ ) is introduced, and the amplitude value of the differential current in a certain section is obtained by the following amplitude value calculation formula (C).

[0167]

[Equation 48]

Further, the flatness determination calculation section 22 determines whether or not the amplitude value obtained by the amplitude value calculation section 25 is equal to or less than a certain value. Is what happens. That is, in this example, it is determined whether or not the amplitude value obtained by the amplitude value calculation unit 25 is equal to or less than a certain value.

Further, the return delay timer 23 has a delay time of about one cycle or more, and is used to make the output of the flatness determination operation unit 22 continuous. Thereby, the output of the differential element 5 can be blocked by the output of the return delay timer 23.

Next, the operation of the differential relay 1 according to the present embodiment will be described. The operation of the differential element 5 is the same as that in the case of FIG. 31, and the description thereof is omitted here. In FIG. 7, the differential current Id derived by the differential current calculator 14 of the differential element 5 is introduced into the exciting rush current countermeasure element 63, and is calculated by the amplitude value calculator 25 to detect flatness. To obtain the amplitude value J.
Then, when the amplitude value J obtained here is equal to or smaller than the predetermined value k, the flatness determination calculation unit 22 generates an output.

On the other hand, the output of the return delay timer 23 is set to NO
Inverted by the T operation circuit 19, the logical product operation circuit 2
By performing a logical product operation with the output of the differential element 5 at 0, the output of the differential element 5 operating by the inrush current can be prevented, and malfunction as the differential relay 1 can be prevented.

Hereinafter, this point will be described more specifically. The difference between the characteristics of the current waveform of the fault current caused by the fault inside the transformer and the current waveform of the exciting inrush current is exactly the same as in the case of the first embodiment, and the description thereof is omitted. Also in the present embodiment, similarly to the case of the first embodiment, it is determined that the excitation rush current is due to the fact that the amplitude value in a certain section in one cycle of the current is small, that is, the flatness is observed. To prevent the differential relay 1 from malfunctioning. That is, the following calculation for obtaining the amplitude value is performed in the amplitude value calculation unit 25 of the excitation inrush current countermeasure element 63.

FIG. 8A shows a value when the exciting inrush current is converted into a digital value of the instantaneous value. In FIG. 8 (a), the instantaneous value of the current i _m, 1 sampling (hereinafter referred to as sp) i _m-1 the instantaneous value of the front,
The instantaneous value before ₂ sp is im _-2 , and the instantaneous value before ₃ sp is im _-3
And put.

[0174] To explain the amplitude value calculated at the instantaneous values of FIG. 8 (a), 4 pieces of the instantaneous values of the given section in one cycle (e.g., i _m ~i _m-3 of section a), the amplitude of the following It is obtained by the value calculation formula (C). The fixed section may be any section that is smaller than the no-current period at the maximum exciting inrush current, and is not particularly limited.

[0175]

[Equation 49]

This value of J is called an amplitude value, and is 1
It represents an amplitude value in a certain section in a cycle, and the amplitude value J becomes zero only when the current waveform in the certain section in one cycle of the differential current is flat.

As in the case of the amplitude value J in the section a, calculation is performed using the past four sp numbers for each sp (in FIG. 8A, the sections b and c are used).
..), It is possible to always see the amplitude value in a certain section, and to determine the individual amplitude values Ja, Jb, Jc... As shown in the calculation result in the amplitude value calculation unit 25 in FIG. Become.

The value of the amplitude value J at the differential current Id due to the exciting rush current having a flat section as shown in FIG. 8B is obtained when the entire calculation section is included in the flat portion of the differential current Id ( In the section a) of FIG. 8A, the value becomes the minimum. Further, when the amplitude value J takes a value smaller than the constant value k, the flatness determination calculation unit 22 generates an output like the calculation result of the flatness determination calculation unit 22 in FIG.

The constant value k is a value for discriminating the fault current from the flat portion of the exciting inrush current, and does not cause erroneous determination due to a loss of DC component due to the current transformer CT or a calculation error of the relay. Value. In the above description, the value representing the flatness has been described based on the amplitude value J, but may be a value represented by the following general formula (Formula (C-1)).

That is, of the calculated differential currents,
Digital amount of four instantaneous value of the electrical angle T of intervals (i _m,
im _-1 , im _-2 , im _-3 ) are introduced, and a value obtained by raising the amplitude value in a certain section to the Nth power is obtained. That is, obtaining the N-th power J ^N amplitude values represented by the (c -1) expression as an amplitude value calculation.

[0181]

[Equation 50]

For example, when N = 2, (c-1)
Equation (C-2) may be used instead of the equation.

(Equation 51)

Then, the N-th power J ^N of the obtained amplitude value is obtained.
Flatness calculating unit 22 that produces an output when is less than or equal to a constant value k
By providing an exciting inrush current countermeasure element 63 having the following structure, the output of which blocks the output of the differential element 5,
The same operation as in the case described above is achieved.

In the present embodiment, four s
Since the calculation is performed using the p number, in the case of a protective relay having a sp interval of T, the calculation interval is 4T. In this case, when the entire calculation section 4T is included in the flat portion of the differential current 1d, the value of the amplitude value J becomes minimum.

Therefore, when the present embodiment is applied to a transformer in which the flat portion of the maximum inrush current is 4 T or more, the fault current can be easily distinguished from the flat portion of the inrush current. .

On the other hand, in the case of protective relays having the same sp interval T, the present embodiment (calculation section 4T) is the same as the second relay described above.
As compared with the embodiment (operation section 3T), there is a feature that the DC component CT is less liable to be lost in the flat portion and the operation error of the relay is less likely to occur. Therefore, when the present embodiment (operation section 4T) is applied to a transformer in which the flat portion of the maximum excitation inrush current is 4T or more, the case where the above-described second embodiment (operation section 3T) is applied. Also, it is possible to more easily distinguish the fault current from the flat portion of the exciting inrush current.

In the present embodiment, the digital amount (i) of four instantaneous values of the electrical current Td at intervals of the electrical angle T out of the differential current Id.
_m , im _-1 , im _-2 , im _-3 ) are introduced to obtain a value obtained by multiplying the amplitude value in a certain section to the Nth power. When the Nth power of this amplitude value is equal to or less than the certain value, the excitation is performed. An excitation inrush current countermeasure element 63 which determines an inrush current and generates an output is provided to detect the flatness of the differential current Id, and the output of the differential element 5 is blocked by the output of the excitation inrush current countermeasure element 63. Because it was
The inrush current and the fault current can be reliably distinguished.
In the above-mentioned conventional technique, it was difficult to apply. Even in the transformer Tr of the electric power system in which the internal fault current includes the harmonic current near the second harmonic, the transformer inrush current will definitely become inoperable, and it will operate reliably in the event of a transformer internal fault. A possible digital protective relay can be obtained.

FIG. 9 is a functional block diagram showing an example of the configuration of a differential relay for protecting a transformer, which is a digital protection relay according to claim 4, wherein the same parts as those in FIG. The description is omitted, and only different portions will be described here. The configuration of the differential element 5 is shown in FIG.
Therefore, a part of the configuration is omitted in FIG.

That is, the differential relay 1 of the present embodiment
As shown in FIG. 9, the excitation inrush current countermeasure element 61 in FIG. 1 is omitted, and a new excitation inrush current countermeasure element 64 is provided instead. The excitation inrush current countermeasure element 64 includes an amplitude value calculator 26, a flatness determination calculator 22, and a return delay timer 23.

Here, the amplitude value calculator 26 calculates the differential current I obtained by the differential current calculator 14 of the differential element 5.
The amplitude value in a certain section of the waveform d is obtained. That is, in this example, of the differential current, the digital quantity of five instantaneous value of the electrical angle T of intervals _{(i m, i m-1} , i m-2,
i _m-3 , i _m-4 ) and the following amplitude value calculation formula (d)
Then, the amplitude value of the differential current in a certain section is obtained.

[0191]

(Equation 52)

Further, the flatness determination calculation section 22 determines whether or not the amplitude value obtained by the amplitude value calculation section 26 is equal to or less than a certain value. Is what happens. That is, in the present example, it is determined whether or not the amplitude value obtained by the amplitude value calculation unit 26 is equal to or less than a certain value.

Further, the return delay timer 23 has a delay time of about one cycle or more, and is used to make the output of the flatness determination operation unit 22 continuous. Thus, the output of the differential element 5 is blocked by the output of the return delay timer 23.

Next, the operation of the differential relay 1 according to the present embodiment will be described. The operation of the differential element 5 is the same as that in the case of FIG. 31, and the description thereof is omitted here. 9, the differential current Id derived by the differential current calculator 14 of the differential element 5 is introduced into the exciting rush current countermeasure element 64, and the amplitude value calculator 26 calculates the flatness by detecting the flatness. Is performed to obtain the amplitude value J. Then, when the amplitude value J obtained here is equal to or smaller than the predetermined value k, the flatness determination calculation unit 22 generates an output.

On the other hand, the output of the recovery delay timer 23 is set to NO
Inverted by the T operation circuit 19, the logical product operation circuit 2
By performing a logical product operation with the output of the differential element 5 at 0, the output of the differential element 5 operating by the inrush current can be prevented, and malfunction as the differential relay 1 can be prevented.

Hereinafter, such a point will be described more specifically. The difference between the current waveforms of the fault current and the inrush current due to the fault inside the transformer is exactly the same as that of the first embodiment, and the description is omitted. Also in the present embodiment, as in the case of the first embodiment, it can be determined that the excitation rush current is due to the fact that the amplitude value in a certain section in one cycle of the current is small, that is, the flatness is observed. This prevents the differential relay 1 from malfunctioning.

That is, the amplitude value calculating section 26 of the exciting rush current countermeasure element 64 performs the following calculation for obtaining the amplitude value. FIG. 10A shows a value when the exciting rush current is converted into a digital value of the instantaneous value. In FIG. 10 (a), the instantaneous value of the current i _m,
The instantaneous value before one sampling (hereinafter, referred to as sp) is i
The instantaneous value before _m-1 and 2sp is set as im _-2 , the instantaneous value before 3sp is set as im _-3 , and the instantaneous value before 4sp is set as im _-4 .

[0198] Figure 10 Describing the amplitude value calculated at the instantaneous values of (a), 5 pieces of the instantaneous values of the given section in one cycle (e.g., i _m ~i _m-4 of the section a), the following ( D) It is obtained by the formula. The fixed section may be any section that is smaller than the no-current period at the maximum exciting inrush current, and is not particularly limited.

[0199]

(Equation 53)

The value of J is called an amplitude value, and is 1
It represents an amplitude value in a certain section in a cycle, and the amplitude value J becomes zero only when the current waveform in the certain section in one cycle of the differential current is flat.

Similar to the amplitude value J in the section a, the calculation is performed using the past five sp numbers for each sp (in FIG. 10A, the sections b,
c.), the amplitude values in a certain section can always be seen, and the values of the individual amplitude values Ja, Jb, Jc... as shown in the calculation result in the amplitude value calculation unit 26 in FIG. Becomes

The value of the amplitude value J in the differential current Id due to the exciting rush current having a flat section as shown in FIG. 10B is obtained when the entire calculation section is included in the flat portion of the differential current Id ( In the section a) of FIG. 10A, the value becomes the minimum. When the amplitude value J takes a value smaller than the constant value k,
The flatness determination calculation unit 22 generates an output like the calculation result of the flatness determination calculation unit 22 in FIG.

The constant value k is a value for discriminating the fault current from the flat portion of the exciting rush current, and does not cause erroneous determination due to a loss of DC component due to the current transformer CT or a calculation error of the relay. Value. In the above description, the value representing the flatness has been described based on the amplitude value J, but may be a value represented by the following general formula (Formula (d-1)).

[0204] That is, among the calculated differential current, digital amount of five instantaneous value of the electrical angle T of intervals (i _m, i
_m−1 , im ₋₂ , im ₋₃ , im ₋₄ ), and the value obtained by raising the amplitude value in a certain section to the Nth power is obtained. That is, obtaining the N-th power J ^N amplitude values represented by the (D -1) below as an amplitude value calculation.

[0205]

(Equation 54)

For example, when N = 2, (d-1)
The equation (d-2) may be used instead of the equation.

[Equation 55]

Then, the N-th power J ^N of the obtained amplitude value is obtained.
Flatness calculating unit 22 that produces an output when is less than or equal to a constant value k
By providing an exciting inrush current countermeasure element 64 having
The same operation as in the case described above is achieved.

In this embodiment, five s
Since the calculation is performed using the p number, in the case of a protective relay having a sp interval of T, the calculation interval is 5T. In this case, when the entire calculation section 5T is included in the flat portion of the differential current Id, the value of the amplitude value J becomes minimum. Therefore, when the present embodiment is applied to a transformer in which the flat portion of the maximum inrush current is 5T or more, it is easy to distinguish between the fault current and the flat portion of the inrush current.

On the other hand, in the case of protective relays having the same sp interval T, the present embodiment (calculation section 5T) is the same as the third relay described above.
As compared with the embodiment (operation section 4T), there is a feature that the DC component CT is less susceptible to loss of the DC component and a calculation error of the relay in the flat portion described above. Therefore, when the present embodiment (operation section 5T) is applied to a transformer in which the flat portion of the maximum excitation inrush current is 5T or more, it is more effective than when the above-described third embodiment (operation section 4T) is applied. Further, it becomes easier to distinguish the fault current from the flat portion of the exciting inrush current.

In the present embodiment, the digital amount (i) of five instantaneous values of the electrical current Td at intervals of the electrical angle T out of the differential current Id.
_m , im ₋₁ , im ₋₂ , im ₋₃ , and im ₋₄ ), and obtains a value obtained by multiplying the amplitude value in a certain section to the Nth power. The Nth power of this amplitude value is equal to or less than a certain value. , An excitation inrush current countermeasure element 64 that determines an excitation inrush current and generates an output.
This is to detect the flatness of d.

Since the output of the differential element 5 is blocked by the output of the exciting rush current countermeasure element 64, the exciting rush current and the fault current can be reliably distinguished. Even for the transformer Tr of the power system in which the internal fault current included the harmonic current near the second harmonic, which was difficult, the transformer inrush current surely became inoperable. A digital protection relay capable of operating reliably can be obtained.

FIG. 11 is a functional block diagram showing a configuration example of a differential relay for protecting a transformer, which is a digital type protection relay according to claim 5, wherein the same parts as those in FIG. The description is omitted, and only different portions will be described here. Note that the configuration of the differential element 5 is exactly the same as that in FIG. 1, and thus a part of the configuration is omitted in FIG. 11.

That is, in the differential relay 1 of the present embodiment, as shown in FIG. 11, the exciting rush current countermeasure element 61 in FIG. 1 is omitted, and a new exciting rush current countermeasure element 65 is provided instead. It is provided with a configuration. The excitation inrush current countermeasure element 65 includes an amplitude value calculator 27 and a flatness determination calculator 2.
2 and a return delay timer 23.

Here, the amplitude value calculator 27 calculates the differential current I obtained by the differential current calculator 14 of the differential element 5.
The amplitude value in a certain section of the waveform d is obtained. That is, in this example, of the differential current, the digital quantity of the six instantaneous value of the electrical angle T of intervals _{(i m, i m-1} , i m-2,
im ₋₃ , im ₋₄ , and im ₋₅ ) are introduced, and the amplitude value of the differential current in a certain section is obtained by the following amplitude value calculation formula (e).

[0215]

[Equation 56]

Further, the flatness determination calculation section 22 determines whether or not the amplitude value obtained by the amplitude value calculation section 27 is equal to or less than a certain value. Is what happens. That is, in this example, it is determined whether or not the amplitude value obtained by the amplitude value calculation unit 27 is equal to or less than a certain value.

Further, the return delay timer 23 has a delay time of about one cycle or more, and is used to make the output of the flatness determination operation unit 22 continuous. Thus, the output of the differential element 5 is blocked by the output of the return delay timer 23.

Next, the operation of the differential relay 1 according to the present embodiment will be described. The operation of the differential element 5 is the same as that in the case of FIG. 31, and the description thereof is omitted here.

In FIG. 11, the differential current Id derived by the differential current calculator 14 of the differential element 5 is introduced to the excitation rush current countermeasure element 65, and the amplitude value calculator 27 detects flatness. Is performed to obtain the amplitude value J.
Then, when the amplitude value J obtained here is equal to or smaller than the predetermined value k, the flatness determination calculation unit 22 generates an output.

On the other hand, the output of the return delay timer 23 is set to NO
Inverted by the T operation circuit 19, the logical product operation circuit 2
By performing a logical product operation with the output of the differential element 5 at 0, the output of the differential element 5 that operates by the exciting rush current is prevented, and malfunction as the differential relay 1 is prevented.

Hereinafter, such a point will be described more specifically. The difference between the characteristics of the current waveform of the fault current caused by the fault inside the transformer and the current waveform of the exciting inrush current is exactly the same as in the case of the first embodiment, and the description thereof is omitted.

In this embodiment, as in the case of the first embodiment, the fact that the amplitude value in a certain section in one cycle of the current is small, that is, the flatness is observed, indicates that the exciting rush current and the inrush current can be reduced. Can be determined, differential relay 1
To prevent malfunction. That is, the excitation inrush current countermeasure element 65
In the amplitude value calculation unit 27, the following calculation for obtaining the amplitude value is performed.

FIG. 12 (a) shows a value when the exciting inrush current is converted into a digital value of the instantaneous value. 12 in (a), i _m, 1 the instantaneous value of the current
The instantaneous value before sampling (hereinafter referred to as sp) is im _-1 , the instantaneous value before 2sp is im _-2 , the instantaneous value before 3sp is im _-3 , and the instantaneous value before 4sp is im _-4. The instantaneous value before ₅ sp is set as im _-5 .

[0224] Figure 12 Describing the amplitude value calculated at the instantaneous values of (a), 6 pieces of the instantaneous values of the given section in one cycle (e.g., i _m ~i _m-5 sections a), the amplitude of the following It is obtained by the value calculation formula (e). The fixed section may be any section that is smaller than the no-current period at the maximum exciting inrush current, and is not particularly limited.

[0225]

[Equation 57]

The value of J is called an amplitude value, and is 1
It represents an amplitude value in a certain section in a cycle, and the amplitude value J becomes zero only when the current waveform in the certain section in one cycle of the differential current is flat. Similarly to the amplitude value J in the section a, the calculation is performed using the past six sp numbers for each sp (sections b, c,... In FIG. 12A), so that the amplitude value in a certain section can be always seen. OK, Figure 12
The individual amplitude values Ja, Jb, Jc... As shown in the calculation result of the amplitude value calculator 27 in (b).

The value of the amplitude value J in the differential current Id due to the inrush current having the flat section as shown in FIG. 12B is obtained when the entire calculation section is included in the flat portion of the differential current Id ( In the section a) of FIG. 12A, the value becomes the minimum. When the amplitude value J takes a value smaller than the constant value k,
The flatness determination calculation unit 22 generates an output like the calculation result of the flatness determination calculation unit 22 in FIG.

The constant value k is a value for discriminating the fault current from the flat portion of the exciting inrush current, and does not cause an erroneous determination due to a loss of DC component due to the current transformer CT or a calculation error of the relay. Value. In the above description, the value representing the flatness has been described based on the amplitude value J, but may be a value represented by the following general formula (formula (e-1)).

[0229] That is, among the calculated differential current, digital amount of five instantaneous value of the electrical angle T of intervals (i _m, i
_m−1 , im ₋₂ , im ₋₃ , im ₋₄ , im ₋₅ ) are introduced, and a value obtained by raising the amplitude value in a certain section to the Nth power is obtained. That is, obtaining the N-th power J ^N amplitude values represented by the formula (e -1) as an amplitude value calculation.

[0230]

[Equation 58]

For example, when N = 2, (e-1)
The equation (e-2) may be used instead of the equation.

[Equation 59]

Then, the N-th power J ^N of the obtained amplitude value is obtained.
Flatness calculating unit 22 that produces an output when is less than or equal to a constant value k
By providing an exciting inrush current countermeasure element 65 having the following, and by blocking the output of the differential element 5 by its output,
The same operation as in the case described above is achieved.

In this embodiment, six s
Since the calculation is performed using the p number, in the case of a protective relay having a sp interval of T, the calculation section is 6T. In this case, when the entire operation section 6T is included in the flat portion of the differential current Id, the value of the amplitude value J becomes minimum. Therefore, when the present embodiment is applied to a transformer in which the flat portion of the maximum inrush current is 6T or more, it is possible to easily distinguish the fault current from the flat portion of the inrush current.

On the other hand, in the case of the protective relays having the same sp interval T, the present embodiment (operation section 6T) is better than the fourth relay.
Compared to the embodiment (operation section 5T), there is a feature that DC components are less likely to be lost by the current transformer CT and a relay calculation error in the flat portion described above. Therefore, when the present embodiment (operation section 6T) is applied to a transformer in which the flat portion of the maximum excitation inrush current is 6T or more, compared to the case where the above-described fourth embodiment (operation section 5T) is applied. In addition, the fault current can be more easily distinguished from the flat portion of the exciting inrush current.

In the present embodiment, of the differential current Id, the digital amount (i) of six instantaneous values at electrical angle T degrees intervals
_m , im ₋₁ , im ₋₂ , im ₋₃ , im ₋₄ , and im ₋₅ ) are introduced, and a value obtained by raising the amplitude value in a certain section to the Nth power is obtained. An excitation inrush current countermeasure element 65 that determines an excitation inrush current and generates an output when the power is equal to or less than a predetermined value is provided to detect flatness of the differential current Id.

Since the output of the differential element 5 is blocked by the output of the exciting rush current countermeasure element 65, the exciting rush current and the fault current can be reliably distinguished. Even for the transformer Tr of the power system in which the internal fault current included the harmonic current near the second harmonic, which was difficult, the transformer inrush current surely became inoperable. A digital protection relay capable of operating reliably can be obtained.

FIG. 13 is a functional block diagram showing a configuration example of a differential relay for protecting a transformer, which is a digital protection relay according to claim 6, wherein the same parts as those in FIG. The description is omitted, and only different portions will be described here. Note that the configuration of the differential element 5 is exactly the same as that in FIG. 1, and thus a part of the configuration is omitted in FIG. 13.

That is, in the differential relay 1 of the present embodiment, as shown in FIG. 13, the exciting rush current countermeasure element 61 in FIG. 1 is omitted, and a new exciting rush current countermeasure element 66 is provided instead. It is provided with a configuration. The excitation inrush current countermeasure element 66 includes amplitude value calculation units 21 and 28, flatness determination calculation units 22 and 29, a logical sum calculation circuit 30, and a return delay timer 23.

Here, the amplitude value calculator 28 calculates the differential current I obtained by the differential current calculator 14 of the differential element 5.
The amplitude value in a certain section of the waveform d is obtained. That is, in this example, of the differential current, the digital quantity of pieces of the instantaneous value 'K of degree intervals' electrical angle _{T (i m ', i m} -1',
im ₋₂ ′, im ₋₃ ′,..., _{im− (} k′− ₁₎ ′) are introduced, and the amplitude value of the differential current in a certain section is calculated by the following amplitude value calculation formula (f). Ask for.

[0240]

[Equation 60]

[0241] Further, the flatness determination calculation section 29 determines whether or not the amplitude value obtained by the amplitude value calculation section 28 is equal to or less than a certain value. Is what happens. On the other hand, the amplitude value calculation unit 21
The configurations of the flatness determination calculation unit 22 and the return delay timer 23 are exactly the same as those in FIG. 1, and thus description thereof is omitted here.

Further, the logical sum operation circuit 30 outputs the logical sum of the output of the flatness judgment operation unit 22 and the output of the flatness judgment operation unit 29. That is, in the present example, it is determined whether or not the amplitude value obtained by the amplitude value calculation unit 21 is equal to or less than a certain value, and whether or not the amplitude value obtained by the amplitude value calculation unit 28 is equal to or less than the certain value. Each is determined, and when at least one of them is equal to or less than a predetermined value, it is determined that the current is an inrush current and an output is generated.

Further, the return delay timer 23 has a delay time of about one cycle or more, and is for making the output of the OR operation circuit 30 continuous. Thus, the output of the differential element 5 is blocked by the output of the return delay timer 23.

Next, the operation of the differential relay 1 according to the present embodiment will be described. The operation of the differential element 5 is the same as that in the case of FIG. 31, and the description thereof is omitted here.

In FIG. 13, the differential current Id derived by the differential current calculator 14 of the differential element 5 is introduced to the exciting rush current countermeasure element 66, and the amplitude value calculator 21 detects flatness. The amplitude value J is obtained by performing a calculation for calculating the flatness, and the amplitude value J ′ is also obtained by performing the calculation for detecting the flatness in the amplitude value calculation unit 28.

When the amplitude value J obtained by the amplitude value calculation section 21 is equal to or smaller than the predetermined value k, the flatness determination calculation section 2
2 produces an output, and when the amplitude value J 'obtained by the amplitude value computing section 28 is equal to or smaller than a predetermined value k', the flatness decision computing section 29 produces an output. Further, the output of the flatness determination operation unit 22 and the output of the flatness determination operation unit 29 are
Logical sum is performed at 0.

On the other hand, the output of the return delay timer 23 is set to NO
Inverted by the T operation circuit 19, the logical product operation circuit 2
By performing a logical product operation with the output of the differential element 5 at 0, the output of the differential element 5 that operates by the exciting rush current is prevented, and malfunction as the differential relay 1 is prevented.

Hereinafter, such a point will be described more specifically. The difference between the characteristics of the current waveform of the fault current caused by the fault inside the transformer and the current waveform of the exciting inrush current is exactly the same as in the case of the first embodiment, and the description thereof is omitted. Also in the present embodiment, similarly to the case of the first embodiment, it is determined that the excitation rush current is due to the fact that the amplitude value in a certain section in one cycle of the current is small, that is, the flatness is observed. To prevent the differential relay 1 from malfunctioning.

Next, the difference between the current waveform of the inrush current when the transformer voltage is applied and the current waveform of the inrush current when the external accident is recovered will be described. FIG. 14 is a waveform diagram showing the difference between the current waveform characteristics of the excitation inrush current (a) when the transformer voltage is applied and the excitation inrush current (b) when the external accident is recovered.

Normally, the excitation inrush current has a section where no current flows due to the saturation of the transformer core during one cycle (no current period). b) During the non-current period, when the protective relay is configured to be affected by the tap position of the transformer,
This is a period close to no current affected by the current passing through the transformer.

Therefore, when a harmonic passes during recovery from an external accident, the portion of the inrush current that the protection relay would otherwise see should be a current-free part, which is affected by the passing harmonic, and as a result, the calculated amplitude value is also zero. Does not take a certain value. FIG. 15 shows the frequency versus gain characteristic of the amplitude value calculation, and shows that the amplitude value calculation of the present method is less susceptible to harmonics as the calculation interval is wider.

A characteristic of the waveform of FIG. 14 is that, in the case of the inrush current (a) when the transformer voltage is applied, the non-current period is short. It is necessary to use not a calculation but an amplitude value calculation with a short calculation section. On the other hand, the excitation inrush current (b) at the time of recovery from an external accident has a feature that the non-current period is wider than that of the excitation inrush current (a) when the transformer voltage is applied. When receiving, it is possible to use an amplitude value calculation with a wider calculation section (which is less susceptible to harmonics) instead of a calculation with a shorter amplitude value in the calculation section.

Therefore, by using both the calculation of the short amplitude value in the calculation section and the calculation of the long amplitude value in the calculation section together, in the case of the inrush current (a) when the transformer voltage is applied, and when the external accident recovery occurs, Even when both the excitation inrush current (b) and the influence of the passing harmonic need to be considered, all the excitation inrush currents can be detected more reliably.

For this reason, when the amplitude value in a wide constant section in one cycle of the current is small, that is, the flatness is observed, and the influence of the current passing through the transformer as in the case of recovery from an accident is obtained. Can be determined as the inrush current, and the malfunction of the differential relay 1 is prevented. That is, the following calculation for obtaining the amplitude value is performed in the amplitude value calculation unit 28 of the excitation rush current countermeasure element 66.

FIG. 16A shows a value obtained by converting the exciting inrush current into a digital value of the instantaneous value. In FIG. 16 (a), i _m 'the instantaneous value of the current,
The instantaneous value before one sampling (hereinafter, referred to as sp) is i
_m-1 ', the instantaneous value before ₂ sp is im _-2 ', the instantaneous value before 3sp is im _-3 ', and the instantaneous value before (K'-1) sp is i.
_{m- (K-1)} ′. To explain the amplitude value calculated at the instantaneous values of FIG. 16 (a), from K 'pieces of instantaneous values (e.g., i _m of the section a' constant interval in one cycle _{~i m- (K-1) '} ) The amplitude value is obtained by the following equation (f).

[0256]

[Equation 61]

Note that the fixed section is not particularly limited as long as it is a section that is smaller than the no-current period at the maximum exciting inrush current at the time of recovery from the accident and can sufficiently reduce the influence of the passing harmonic. This value of J 'is called an amplitude value, and represents an amplitude value in a certain section in one cycle of the differential current. The more flat the current waveform in the certain section in one cycle of the differential current becomes, The amplitude value J becomes smaller.

As in the case of the amplitude value J 'of the section a, the calculation is performed using the past K sp numbers for each sp (sections b, c... In FIG. And the individual amplitude values Ja ′, Jb ′, J as shown in the calculation result in the amplitude value calculation unit 28 in FIG.
c ′...

The value of the amplitude value J 'at the differential current Id due to the exciting rush current having a flat section as shown in FIG.
When all the calculation sections are included in a period close to no current of the differential current Id (section a in FIG. 16A), the value becomes minimum. Also, when the amplitude value J 'takes a value smaller than the constant value k', the flatness determination calculation unit 29 generates an output like the calculation result of the flatness determination calculation unit 29 in FIG.

The constant value k is a value for discriminating the fault current from the flat portion of the exciting rush current, and the DC current loss due to the current transformer CT, the calculation error of the relay, and the passing through the transformer. This value does not result in erroneous determination due to the influence of harmonics. In the above description, the value representing the flatness has been described based on the amplitude value J ′. However, the following general formula ((he-
1) It may be a value represented by the formula).

[0261] That is, among the calculated differential current, digital amount of pieces of the instantaneous value 'K of degree intervals' electrical angle _{T (i m', i m} -1 ', i m-2', ..., _{im- (K-1)} ') is introduced, and a value obtained by raising the amplitude value in a certain section to the Nth power is obtained. That is, the N-th power J ′ of the amplitude value represented by the following equation (F-1)
^N is calculated as an amplitude value calculation.

[0262]

(Equation 62)

[0263]

[Equation 63] For example, when N = 2, the expression (F-2) may be used instead of the expression (F-1).

Then, the N-th power J 'of the obtained amplitude value is obtained.
By providing an exciting rush current countermeasure element 66 having a flatness determination calculating unit 29 that generates an output when ^N is equal to or less than a constant value k ′, and by blocking the output of the differential element 5 by the output, It has a similar effect.

In the present example, the processing of the amplitude value of the digital quantity of the K ′ instantaneous values of the electrical angle T ′ degree interval is performed in contrast to the processing of the amplitude value of the K instantaneous value of the electrical angle T degree interval. Since only the contents are added, the present invention can be applied to all of the first to fifth aspects.

In the present embodiment, of the differential current Id, the digital amount (i) of K instantaneous values of the electrical angle T-degree intervals is used.
_{m, i m-1, i} m-2, ..., i m- (k-1)) and the digital quantity of pieces of the instantaneous value 'K of degree intervals' electrical angle T (i _m',
im _-1 ', im _-2 ',..., _{im- (k-1)} ') are introduced, and the values J and J' obtained by raising the amplitude value of a certain section to the Nth power are obtained. When at least one of the N-th powers of the values J and J 'is equal to or smaller than a certain value, the excitation inrush current is determined and the output is provided with an excitation inrush current countermeasure element 66 for detecting flatness of the differential current Id. is there.

Since the output of the differential element 5 is blocked by the output of the exciting rush current countermeasure element 66, the exciting rush current and the fault current can be reliably distinguished from each other. Even for the transformer Tr of the power system in which the internal fault current included the harmonic current near the second harmonic, which was difficult, the transformer inrush current surely became inoperable. A digital protection relay capable of operating reliably can be obtained.

FIG. 17 is a functional block diagram showing a configuration example of a differential relay for protecting a transformer, which is a digital protection relay according to claim 7, wherein the same parts as those in FIG. The description is omitted, and only different portions will be described here. Note that the configuration of the differential element 5 is exactly the same as that in FIG. 1, and thus a part of the configuration is omitted in FIG. 17.

That is, in the differential relay 1 of the present embodiment, as shown in FIG. 17, the exciting rush current countermeasure element 61 in FIG. 1 is omitted, and a new exciting rush current countermeasure element 67 is provided instead. It is provided with a configuration. The excitation inrush current countermeasure element 67 includes an amplitude value calculation unit 21 and a flatness determination calculation unit 2.
2, operation delay timer 31, and return delay timer 23
It consists of

Here, the amplitude value calculator 21 calculates the differential current I obtained by the differential current calculator 14 of the differential element 5.
The amplitude value in a certain section of the waveform d is obtained. That is, in this example, of the differential current, the digital quantity of the K instantaneous value of the electrical angle T of intervals _{(i m, i m-1} , i m-2,
, i _m−3 ,..., i _{m− (k−1)} ), and the amplitude value in one section of the differential current is obtained by the amplitude value calculation formula (a).

[0271]

[Equation 64]

Also, the flatness determination calculation section 22 determines whether or not the amplitude value obtained by the amplitude value calculation section 21 is equal to or smaller than a predetermined value. Is what happens. That is, in this example, it is determined whether or not the amplitude value obtained by the amplitude value calculation unit 21 is equal to or less than a certain value.

Further, the operation delay timer 31 is set to 1 sp
It has the above-described delay time, and is for eliminating the sporadic output (for example, 1 sp output) of the flatness determination calculation unit 22. On the other hand, the return delay timer 23 has a delay time of about one cycle or more, and is for making the output of the operation delay timer 31 continuous. Thereby, the return delay timer 2
The output of 3 blocks the output of differential element 5.

Next, the operation of the differential relay 1 according to the present embodiment will be described. The operation of the differential element 5 is the same as that in the case of FIG. 31, and the description thereof is omitted here. In FIG. 17, the differential current Id derived by the differential current calculator 14 of the differential element 5 is introduced into the exciting rush current countermeasure element 67, and is calculated by the amplitude value calculator 21 to detect flatness. To obtain the amplitude value J. Then, when the amplitude value J obtained here is equal to or smaller than the predetermined value k, the flatness determination calculation unit 22 generates an output.

On the other hand, the output of the flatness determination operation section 22 is inverted by the NOT operation circuit 19 after passing through the operation delay timer 31 and the return delay timer 23, and further, the differential element 5 is output by the AND operation circuit 20. By performing a logical AND operation with the output of the differential element 5, the differential element 5 that operates with the exciting inrush current
Is prevented, and a malfunction as the differential relay 1 is prevented.

Hereinafter, such a point will be described more specifically. The difference between the characteristics of the current waveform of the fault current caused by the fault inside the transformer and the current waveform of the exciting inrush current is exactly the same as in the case of the first embodiment, and the description thereof is omitted. Also in the present embodiment, similarly to the case of the first embodiment, it is determined that the excitation rush current is due to the fact that the amplitude value in a certain section in one cycle of the current is small, that is, the flatness is observed. To prevent the differential relay 1 from malfunctioning.

That is, the amplitude value calculating section 21 of the excitation inrush current countermeasure element 67 performs the following calculation for obtaining the amplitude value. FIG. 18 (a) shows a value when the fault current inside the transformer is converted into a digital value of the instantaneous value. In FIG. 18 (a), the instantaneous value of the current i _m, 1 sampling (hereinafter referred to as sp) before the instantaneous value _{i m-1, i m-} 2 the instantaneous value before 2sp, 3sp previous instantaneous value Is _im-3 , ..., the instantaneous value before (K-1) sp is i
Put _{m- (K-1)} .

[0278] To explain the amplitude value calculated at the instantaneous values of FIG. 18 (a), of K instantaneous values of certain intervals during one cycle (e.g., the section _{a i m ~i m- (K-} 1)) Is determined by the following equation (a). The fixed section may be any section that is smaller than the no-current period at the maximum exciting inrush current, and is not particularly limited.

[0279]

[Equation 65]

The value of J is referred to as an amplitude value, and is equal to 1 of the differential current.
It represents an amplitude value in a certain section in a cycle, and the amplitude value J becomes zero only when the current waveform in the certain section in one cycle of the differential current is flat.

As in the case of the amplitude value J in the section a, calculation is performed using the past K sp numbers for each sp (in FIG. 18A, the sections b,
c.), the amplitude values in a certain section can always be seen, and the values of the individual amplitude values Ja, Jb, Jc... as shown in the calculation result in the amplitude value calculation unit 21 in FIG. Becomes

In the differential current Id due to the fault current inside the transformer as shown in FIG. 18 (b), the entire calculation section does not become a flat portion, and the value of the amplitude value J is always large. Also,
When the amplitude value J takes a value smaller than the constant value k, the flatness determination calculation unit 22 shown in FIG.
Produces an output like the result of the operation at.

The constant value k is a value for discriminating the fault current from the flat portion of the inrush current, and does not cause erroneous determination due to a loss of DC component due to the current transformer CT or a calculation error of the relay. Value. For most fault currents, as described above, the value of the amplitude value J is always large, the amplitude value J does not take a value smaller than the constant value k, and the flatness determination calculation unit 22 does not generate an output.

However, due to the relationship between the harmonics at the time of the accident and the sp timing, the instantaneous values in the operation section become substantially equal, and the operation result of the amplitude value operation unit 21 is accidentally irrespective of the accident current, as shown by Ja. It is also conceivable that the size becomes smaller and the flatness determination calculation unit 22 instantaneously generates an output. However, since the calculation result of the flatness determination calculation unit 22 is sporadic and does not continue, even when such an instantaneous output is generated, this output is input to the operation delay timer 31, and
Since the operation is delayed by a predetermined time, the operation delay timer 3
1 produces no output.

Therefore, even in such a case, the operation delay timer 31 does not generate an output, but the output of the return delay timer 31 is inverted by the NOT operation circuit 19 so that the NOT operation circuit 19 always generates an output, and the differential element By performing a logical product operation with the output of the differential element 5 in the logical product operation circuit 20, the output of the differential element 5 operating with the fault current is not blocked, and the differential relay 1 can operate normally. it can. The time of the operation delay timer 31 is not limited to 1 sp, but may be 1 sp or more as long as it does not hinder flat detection of the inrush current.

In this embodiment, the digital amount (i) of K instantaneous values of the differential current Id at electrical angle T-degree intervals is used.
_m , im _-1 , im _-2 ,..., _{im- (k-1)} ), and obtains a value obtained by multiplying the amplitude value in a certain section to the Nth power. As described above, the excitation inrush current countermeasure element 67 which determines an excitation inrush current when the value is equal to or less than the predetermined value and generates an output is provided to detect the flatness of the differential current Id.

Since the output of the differential element 5 is blocked by the output of the exciting rush current countermeasure element 67, the exciting rush current and the fault current can be reliably distinguished from each other. Even for the transformer Tr of the power system in which the internal fault current included the harmonic current near the second harmonic, which was difficult, the transformer inrush current surely became inoperable. A digital protection relay capable of operating reliably can be obtained.

FIG. 19 is a functional block diagram showing an example of the configuration of a differential relay for protecting a transformer, which is a digital protection relay according to claim 8, and the same parts as those in FIG. The description is omitted, and only different portions will be described here. Note that the configuration of the differential element 5 is exactly the same as that in FIG. 1, and thus a part of the configuration is omitted in FIG. 19.

That is, in the differential relay 1 according to the present embodiment, as shown in FIG. 19, the excitation inrush current countermeasure element 61 in FIG. 1 is omitted, and a new excitation inrush current countermeasure element 68 is provided instead. It is provided with a configuration. The excitation inrush current countermeasure element 68 includes an amplitude value calculation unit 21 and a flatness determination calculation unit 2.
2, a shift operation unit 32, an AND operation circuit 33, and a return delay timer 23.

Here, the amplitude value calculation section 21 and the flatness determination calculation section 22 have the same functions as those of the first embodiment. The shift operation unit 32
Is to delay the output of the flatness determination calculation unit 22 by one cycle.

Further, the AND operation circuit 33 outputs the output (current output) of the flatness judgment operation section 22 and the shift operation section 3
The return delay timer 23 has a delay time of about one cycle or more, and is used to make the output of the AND operation circuit 33 continuous. Things.

Next, the operation of the differential relay 1 according to the present embodiment will be described. The operation of the differential element 5 is the same as that in the case of FIG. 31, and the description thereof is omitted here. In FIG. 19, the differential current Id derived by the differential current calculation unit 14 of the differential element 5 is introduced into the exciting rush current countermeasure element 68, and the amplitude value calculation unit 21 calculates the differential current Id based on the above equation (A). Calculation is performed, and each differential current Id
The amplitude value J of a certain section at p is calculated. Further, when the amplitude value J becomes equal to or less than the predetermined value k, the flatness determination calculation unit 22 determines that the current is an inrush current, and outputs an output.

The excitation inrush current has a periodicity of 1 between a period in which current flows and a period in which current does not flow, due to the relationship of transformer core saturation.
Occurs every cycle. For this reason, the output of the flatness determination calculation unit 22 based on the inrush current is always sent once every cycle, and the output is an intermittent output having a periodicity every cycle.

On the other hand, the fault current is a superimposition of the fundamental wave current or the unspecified harmonic current and does not cause a no-current period, but is rarely a transient flat portion due to the superimposition of harmonics. It is conceivable to have FIG. 20 is a diagram illustrating an example of a case where the fault current has a transient flat portion. In the portion A of the differential current Id, the amplitude value J becomes equal to or less than a predetermined value k, and the flatness determination calculation unit 22 Sends out the output,
At this time, the output of the flatness determination calculation unit 22 does not have periodicity.

Then, the output of the flatness determination calculation section 22 is delayed by one cycle by the shift calculation section 32, and the output of the flatness determination calculation section 22 which is the current determination result and the shift calculation section 32 which is the determination result of one cycle before are output. By performing the AND operation with the output by the AND operation circuit 33, the periodicity of the flat portion in the differential current Id can be seen.

FIG. 21 is a diagram showing an example of the detection of the periodicity in the excitation inrush current and the fault current. In the excitation inrush current (a), an AND operation is performed for the periodic output of the flatness determination operation unit 22. Although the output of the circuit 33 is generated, the output of the AND operation circuit 33 is not generated in the fault current (b) because of the sporadic output of the flatness determination operation unit 22.

Since the result of the AND operation in the AND operation circuit 33 based on the inrush current is an intermittent output, the output is output from the excitation inrush current countermeasure element 68 after being made continuous by the return delay timer 23.

As a result, the exciting inrush current countermeasure element 68 operates reliably against the inrush current, and the differential relay 1
In addition, an unnecessary output of the exciting rush current countermeasure element 68 does not occur even for an accident current in which a transient flat portion occurs, and the differential relay 1 can operate normally.

The time delayed by the shift operation section 32 is not limited to one cycle, but may be one cycle or more, and may be a positive multiple cycle capable of determining the continuity characteristic of the inrush current. In this embodiment, when discriminating between a case where a single output of the flatness determination calculation unit is generated by the fault current and a case where the output of the flatness determination calculation unit is generated by the inrush current, the periodicity is detected as a means. A shift operation unit 32 is provided, and the flatness judgment unit 2 which is the current judgment result is provided.
This is performed by a logical operation of the output of the shift operation unit 32 and the output of the shift operation unit 32 which is the result of the judgment one cycle before. Therefore, this type of determination method is applicable to all of the first to fifth aspects.

In the present embodiment, of the differential current Id, the digital quantity (i) of K instantaneous values at intervals of electrical angle T degrees is shown.
_m , im _-1 , im _-2 , ..., _{im- (K-1)} ), and obtains a value obtained by multiplying the amplitude value in a certain section to the Nth power. The output generated when the following condition is satisfied is compared with the output of the flatness determination operation 22 one cycle before, and when the AND condition of both is satisfied, the excitation inrush current countermeasure element 68 which determines the excitation inrush current and generates an output is determined. In addition, the flatness of the differential current Id is detected.

Since the output of the differential element 5 is blocked by the output of the exciting rush current countermeasure element 68, the exciting rush current and the fault current can be reliably distinguished. It is difficult for the transformer Tr of the power system in which the internal fault current includes the harmonic current near the second harmonic to be surely inoperable by the transformer inrush current, and the internal fault current is difficult. A digital protection relay that can sometimes operate reliably can be obtained.

FIG. 22 is a functional block diagram showing a configuration example of a differential relay for protecting a transformer, which is a digital protection relay according to the ninth aspect. The same parts as those in FIG. The description is omitted, and only different portions will be described here. Note that the configuration of the differential element 5 is exactly the same as that in FIG. 1, and thus a part of the configuration is omitted in FIG. 22.

That is, in the differential relay 1 of the present embodiment, as shown in FIG. 22, the exciting rush current countermeasure element 61 in FIG. 1 is omitted, and a new exciting rush current countermeasure element 69 is provided instead. It is provided with a configuration. The excitation inrush current countermeasure element 69 includes an amplitude value calculator 21 and a shift calculator 34.
A maximum value detection calculation unit 35, a flatness determination calculation unit 36,
A return delay timer 23 is provided.

Here, the amplitude value calculator 21 has the same function as in the case of the first embodiment already described. The shift calculator 34 is for delaying the value of the amplitude value J output from the amplitude value calculator 21 by one cycle. On the other hand, the maximum value detection calculation unit 35
Is compared with the amplitude value J output from the shift operation unit 34, and the larger amplitude value J _MAX is output.

Further, the flatness determination calculation section 36 determines whether or not the amplitude value J _MAX output from the maximum value detection calculation section 35 is smaller than a predetermined value k, and outputs the output when it is smaller than the predetermined value k. Occurs. Furthermore, the return delay timer 23
A delay time of about a cycle or more, and
6 to make the output 6 continuous.

Next, the operation of the differential relay 1 according to the present embodiment will be described. The operation of the differential element 5 is the same as that in the case of FIG. 31, and the description thereof is omitted here. In FIG. 22, the differential current Id derived by the differential current calculator 14 of the differential element 5 is introduced to the exciting rush current countermeasure element 69, and the amplitude value calculator 21 calculates the differential current Id based on the equation (A) described above. Calculation is performed, and each differential current Id
The amplitude value J of a certain section at p is calculated.

The current amplitude value output from the amplitude value calculating section 21 is defined as J (current), the amplitude value J (current) is delayed by one cycle by the shift calculating section 34, and the delayed amplitude value is determined as J (current). (One cycle before). on the other hand,
In the maximum value detection calculation unit 35, these amplitude values J (current)
And comparing the amplitude value J (1 cycle before), the amplitude value of the larger one is outputted as the J _MAX. In addition, when the amplitude value J _MAX output from the maximum value detection unit 35 becomes equal to or smaller than the predetermined value k, the flatness determination calculation unit 36 determines that the current is an inrush current, and outputs the output.

The excitation inrush current has a periodicity between a period in which the current flows and a period in which the current does not flow, every cycle, due to the relationship between the transformer core saturation. For this reason, the amplitude value J calculated by the amplitude value calculation unit 21 also has an output having a periodicity that is minimized every cycle, and the amplitude value J (current) at the present time and the amplitude value J (1) at the previous cycle are obtained. (Before the cycle) is an equal value.

As a result, since the maximum value detection calculation section 35 outputs the amplitude value J (current) (= J (one cycle before)) as it is, the output of the flatness determination calculation section 36 is output every cycle. This is an intermittent output with periodicity. The output of the flatness determination calculation unit 36 is made continuous by the return delay timer 23 and used as the output of the excitation inrush current countermeasure element 69, so that malfunction of the differential relay 1 can be prevented.

On the other hand, the fault current is a superimposition of the fundamental wave current or the unspecified harmonic current, and does not cause a no-current period. It is possible to have a part. FIG. 23 is a diagram illustrating an example of a case where the fault current has a transient flat portion, and illustrates a change in the amplitude value J output from the amplitude value calculating section 21.

FIG. 23A shows the output of the amplitude value calculator 21 and the flatness determination calculator 2 in the first embodiment.
23, the amplitude value becomes equal to or smaller than the predetermined value k at the time point B, and the flatness determination calculation unit 22 transiently outputs a single shot as shown in FIG. On the other hand, FIG.
Is the amplitude value J of the output of the amplitude value calculation unit 21 in FIG.
This is the output (amplitude value J _MAX ) of the maximum value detection calculation unit 35 obtained by comparing (current) and the output with the amplitude value J (one cycle before) obtained through the shift calculation unit 34.

For example, the value of the amplitude value B at the present time in FIG. 23A is compared with the value of the amplitude value C one cycle before, and the larger one (here, C) is determined. 23
Since the output value is output as the value of the amplitude value J _MAX of the maximum value detection calculation unit 35 of (c), the flatness determination calculation unit 36 does not operate, and the exciting rush current countermeasure element 69 does not generate an output. Can perform normal operation.

The time delayed by the shift operation section 34 is not limited to one cycle, but may be a positive multiple cycle in accordance with the periodicity of the flat portion of the inrush current.
Further, if the time does not hinder the flatness detection as well as the periodicity, a comparison with 1 sp or earlier may be performed and the larger amplitude value may be used. In the present embodiment, as in the case of claim 8, when discriminating between the fault current and the exciting inrush current, the current amplitude value is compared with the amplitude value delayed by one cycle, and the maximum value is calculated. Is output, and when the maximum value is equal to or less than a predetermined value k, it is determined that the output is a single-shot output. Therefore, this type of determination method is described in claims 1 to 5
Applicable to all.

In the present embodiment, of the differential current Id, the digital amount (i) of K instantaneous values of the electrical angle T degrees interval is set.
_m , im _-1 , im _-2 ,..., _{im- (K-1)} ), and the value obtained by multiplying the amplitude value in a certain section to the Nth power is obtained. By comparing the previous amplitude value with the Nth power, when the larger amplitude value becomes equal to or less than a predetermined value k, it is determined as an exciting inrush current and an exciting inrush current countermeasure element 6 which produces an output
9 to detect the flatness of the differential current Id.

Since the output of the differential element 5 is blocked by the output of the exciting rush current countermeasure element 69, the exciting rush current and the fault current can be reliably distinguished. It is difficult for the transformer Tr of the power system in which the internal fault current includes the harmonic current near the second harmonic to be surely inoperable by the transformer inrush current, and the internal fault current is difficult. A digital protection relay that can sometimes operate reliably can be obtained.

FIG. 25 is a circuit diagram showing a configuration example in which the digital protection relay according to claim 10 is applied to a power transformer. In FIG. 25, the power system power supply G includes:
The transformer Tr to be protected is connected via the circuit breaker CB. Further, main transformers CT1 and CT2 for extracting an alternating current for each phase are provided with the transformer Tr interposed therebetween.

On the other hand, an instrument transformer PT for extracting an AC voltage for each phase is provided at any one terminal of the transformer Tr. Further, alternating currents I1 and I2 extracted by the main current transformers CT1 and CT2 and the instrument transformer PT,
The AC voltage V1 is introduced to the differential relay 80, and operates in the event of an internal fault of the transformer Tr to shut off the circuit breaker CB, thereby protecting the transformer Tr.

FIG. 24 is a functional block diagram showing an example of the configuration of a differential relay for protecting a transformer, which is a digital protection relay according to the present embodiment. A description thereof will be omitted, and only different portions will be described here. That is, as shown in FIG. 24, the differential relay 80 of the present embodiment has an input transformer 37 and an A / D converter 3 added to the differential relay 1 of FIG. Omit the inrush current suppression element 61 at
Instead, the configuration is provided with a new exciting rush current countermeasure element 70.

The input transformer 37 converts the AC voltage V1 extracted by the instrument transformer PT into an appropriate magnitude. Also, the A / D converter 3 includes the AC currents I1, I2 extracted by the input transformer 2 and the input transformer 37.
The AC voltage V1 extracted in the step (1) is sampled at regular time intervals and converted into a digital quantity.

Further, the excitation inrush current countermeasure element 70 includes an amplitude value computing section 21, a flatness decision computing section 22, a voltage value computing section 38, a voltage value decision computing section 39, and a logical product computing circuit 4
0 and a return delay timer 23. Here, the amplitude value calculation unit 21, the flatness determination calculation unit 22, and the return delay timer 23 have the same functions as those in the first embodiment.

On the other hand, the voltage value calculating section 38 extracts the fundamental wave component 1f from the electric quantity v1 and calculates the amplitude value | V |. In addition, the voltage value determination calculation section 39 includes a voltage value calculation section 38.
It is determined whether or not the amplitude value | V |, which is the output of, is larger than a predetermined value kv, and an output is generated when the amplitude value | V | is larger than the predetermined value kv. Further, the output of the recovery delay timer 23 and the output of the voltage value judgment operation unit 39 are
Logical AND is performed at 0.

On the other hand, the output of the AND operation circuit 40 is
Inverted by the operation circuit 19,
By performing an AND operation with the output of the differential element 5 in
Blocking the output of the differential element 5 operating with the inrush current of the excitation,
A malfunction as the differential relay 80 is prevented.

Next, the operation of the differential relay 80 according to the present embodiment will be described. The operation of the differential element 5 is the same as that in the case of FIG. 31, and the description thereof is omitted here. In FIG. 24, the differential current Id derived by the differential current calculator 14 of the differential element 5 is introduced into the excitation rush current countermeasure element 70, and is calculated by the amplitude value calculator 21 to detect flatness. And the amplitude value J is obtained.

When the obtained amplitude value J is equal to or smaller than the predetermined value k, the flatness determination calculation section 22 generates an output, and the output of the flatness determination calculation section 22 is made continuous by the return delay timer 23. .

On the other hand, as shown in FIG. 25, the voltage V1 at any one terminal of the transformer is converted to an appropriate magnitude via the instrument transformer PT. Further, as shown in FIG. 24, the AC voltage V1 extracted by the instrument transformer PT
Is further converted into an appropriate size by the input transformer 37, and is then introduced into the A / D converter 3.

Further, the A / D converter 3 samples the AC voltage V1 at fixed time intervals and converts it into a digital quantity v1. The v1 converted into the digital quantity is introduced into the voltage amplitude value calculator 38, and its fundamental wave component 1f
After calculating the amplitude value | V |, the voltage value determination calculation unit 39 determines whether or not the amplitude value | V | is larger than a predetermined value kv. The decision operation section 39 produces an output.

The output of the voltage value judging operation section 39 is ANDed with the output of the return delay timer 23 by the AND operation circuit 40 and then inverted by the NOT operation circuit 19.
Further, by performing an AND operation with the output of the differential element 5 in the AND operation circuit 20, the output of the differential element 5 operating by the inrush current is prevented, and the malfunction as the differential relay 1 is prevented. be able to.

Hereinafter, such a point will be described more specifically. The excitation inrush current has a periodicity between a period in which the current flows and a period in which the current does not flow, for each cycle due to the relationship of the transformer core saturation. For this reason, the output of the flatness determination calculation unit 22 based on the inrush current is always sent once every cycle, and the output is an intermittent output having a periodicity every cycle.

Therefore, the output of the return delay timer 23 having a delay time of about one cycle or more is always transmitted. Further, when a transformer voltage is applied such that an inrush current occurs, the amplitude value of the voltage is sufficiently large, so that the voltage amplitude value | V |
Always takes a value larger than the predetermined value kv. As a result, | V | ≧ kv is always satisfied in the voltage value determination operation 39, and the output of the voltage value determination operation 39 is also constantly transmitted.

The voltage amplitude value may be any known algorithm for calculating an amplitude value. For example, the instantaneous value at the present time is represented by v _m , and the instantaneous value before one sampling (hereinafter, referred to as sp) is represented by v _m− The instantaneous value before ₁ , 2 sp is v _m−2 ,.
When the instantaneous value before sp is set as v _m-5 ,
It is calculated by an equation.

[0331]

[Equation 66]

The output of the return delay timer 23 and the output of the voltage value judgment operation 39 are
Since the AND operation is performed at 0, the inrush current suppression element 70 always generates an output. Since the output of the excitation inrush current countermeasure element 70 is inverted by the NOT operation circuit 19,
The OT operation circuit 19 does not always generate an output, and can always block the output of the AND operation circuit 20. Therefore, it is possible to prevent the differential relay 80 from malfunctioning due to the inrush current.

On the other hand, in the case of an internal fault, a fundamental current or an unspecified harmonic current is superimposed. Since the terminal voltage is greatly reduced, the amplitude value | V |, which is the output of the voltage amplitude value calculation unit, is smaller than the predetermined value kv, and as a result, the voltage value determination calculation 39 does not always generate an output.

Therefore, the output of the return delay timer 23 and the output of the voltage value judgment operation 39 are
The logical AND is performed at 0, and the exciting inrush current countermeasure element 70 does not always generate an output. Since the output of the excitation inrush current countermeasure element 70 is inverted by the NOT operation circuit 19,
The T operation circuit 19 always produces an output, and the AND operation circuit 20
The differential relay 80 can operate normally without blocking the output of the differential relay 80. In this embodiment, as a means for discriminating between an internal fault and an exciting inrush current, the terminal voltage of the transformer is greatly reduced during an internal fault, whereas the amplitude value of the voltage is a predetermined value during the exciting inrush current. This is based on the above. Therefore, this type of determination method is described in claim 1
To claim 9.

As described above, in the present embodiment, the difference between the waveforms of the transformer inrush current and the transformer internal fault current, that is, the excitation inrush current is caused by the saturation of the magnetic flux of the transformer core during one cycle. While there is always a flat section where the current flows and the saturation of the transformer core is released and the current does not flow, the fault current has a flat section in the fixed section due to the fundamental current or the superposition of an unspecified number of harmonic currents. The voltage difference between when the transformer inrush current occurs and when a transformer internal fault current occurs, i.e., when the magnetizing inrush current occurs, the voltage amplitude value is large, but when the fault current occurs, the voltage amplitude value is small. It focuses on both.

[0336] Therefore among the differential current Id, a digital quantity of the K instantaneous value of the electrical angle T of intervals _{(i m, i m-1} ,
im _-2 ,..., _{im- (k-1)} ), and a value obtained by raising the amplitude value in a certain section to the Nth power is obtained. Is equal to or more than a predetermined value kv, the excitation inrush current countermeasure element 70 which determines an excitation inrush current and generates an output when the two conditions are satisfied. 5
Output is blocked.

Therefore, it is possible to reliably distinguish the inrush current from the exciting current and the fault current, and it has been difficult to apply the above-described conventional technique. Therefore, the internal fault current includes a harmonic current near the second harmonic in the power system. The transformer Tr is also reliably inactivated by the transformer inrush current, and a digital protection relay capable of reliably operating in the event of a transformer internal accident can be obtained.

FIG. 26 is a functional block diagram showing a configuration example of a differential relay for protecting a transformer, which is a digital protection relay according to claim 11, wherein the same parts as those of FIG. The description will be omitted, and only different portions will be described here. That is, the differential relay 80 of the present embodiment
26, as shown in FIG. 26, the excitation inrush current countermeasure element 70 in the differential relay 80 of FIG. 24 is omitted, and a new excitation inrush current countermeasure element 71 is provided instead.

Further, the excitation inrush current countermeasure element 70 includes the amplitude value calculation units 21 and 41, the flatness determination calculation unit 22, the voltage value determination calculation unit 42, the return delay timer 23, and the logical product calculation circuit 43. Has become. Here, the amplitude value calculation unit 21, the flatness determination calculation unit 22, and the return delay timer 2
Reference numeral 3 has a function similar to that of the embodiment of FIG.

Here, the amplitude value calculator 41 calculates the AC voltage v
The amplitude value in a certain section of the waveform 1 is obtained. In this example, of the AC voltage, the same K as the K of the amplitude value calculation unit 21 at the same electrical angle T degree interval as the T of the amplitude value calculation unit 21
Digital amount of pieces of the instantaneous value _{(v m, v m-1} , v m-2, v
_m-3 , ..., v _{m- (k-1)} ) and the amplitude value calculation formula (g)
Then, the amplitude value in a certain section of the AC voltage is obtained.

[0341]

[Equation 67]

The voltage value judging and calculating section 42 judges whether or not the amplitude value obtained by the amplitude value calculating section 41 is equal to or more than a predetermined value. Is caused. Further, the output of the return delay timer 23 and the output of the voltage value judgment operation unit 42 are ANDed by the AND operation circuit 43.

On the other hand, the output of the AND operation circuit 43 is NOT
Inverted by the operation circuit 19,
By performing an AND operation with the output of the differential element 5 in
Blocking the output of the differential element 5 operating with the inrush current of the excitation,
A malfunction as the differential relay 80 can be prevented.

Next, the operation of the differential relay 80 according to the present embodiment will be described. The operation of the differential element 5 is the same as that in the case of FIG. 31, and the description thereof is omitted here. In FIG. 26, the differential current Id derived by the differential current calculator 14 of the differential element 5 is introduced into the exciting rush current countermeasure element 71, and is calculated by the amplitude value calculator 21 to detect flatness. Is performed to obtain the amplitude value J. Then, when the obtained amplitude value J is equal to or smaller than the predetermined value k, the flatness determination calculation unit 22 is output.

On the other hand, as in the case of the embodiment of FIG. 24, the voltage V1 at any one terminal of the transformer is converted into an appropriate voltage via a transformer PT, and The AC voltage V1 extracted by the PT is further converted to an appropriate magnitude by the input transformer 37,
The A / D converter 3 samples the AC voltage V1 at fixed time intervals and converts it into a digital quantity v1.

[0346] The v1 converted into the digital quantity is introduced into the voltage amplitude value calculation unit 41, and is subjected to calculation for obtaining the amplitude value in the same calculation section as the amplitude value calculation unit 21, thereby obtaining the amplitude value Jv. . Then, when the amplitude value Jv obtained here is equal to or larger than the predetermined value kv, the voltage value determination calculation section 42 generates an output.

Also, the output of the voltage value judgment operation section 42 is ANDed with the output of the return delay timer 23 by the AND operation circuit 43 and then inverted by the NOT operation circuit 19,
Further, by performing an AND operation with the output of the differential element 5 in the AND operation circuit 20, the output of the differential element 5 operating by the inrush current is prevented, and the malfunction as the differential relay 1 is prevented. .

Hereinafter, this point will be described more specifically. First, the characteristics of the voltage waveform when the exciting inrush current occurs will be described. FIG. 27 is a waveform diagram showing the characteristics of the current waveform of the excitation inrush current (a) and the voltage waveform (b) when the excitation inrush current occurs.

In FIG. 27, the voltage waveform (b) in the section where the exciting rush current (a) is flowing has a small voltage due to a voltage drop due to the relationship between the exciting rush current and the reactance of the transformer. In the excitation inrush current (a), there is always a section where no current flows due to the saturation of the transformer core during one cycle (no current period), and in this case, the voltage inrush current flows in the voltage waveform (b). Therefore, there is no influence of the voltage drop, and the amplitude becomes large.

For this reason, by calculating the amplitude value in a fixed section in one cycle of the voltage in the same fixed section (calculation section) as the amplitude value calculating section 21, the large voltage in the no-current period can be used. The fact that the voltage when the exciting inrush current is generated is sufficiently large can be more reliably detected, and it can be determined that the exciting inrush current is present, thereby preventing the differential relay 80 from malfunctioning.

That is, the amplitude value calculating section 41 of the excitation inrush current countermeasure element 71 performs the following calculation for obtaining the amplitude value. FIG. 27 (b) shows a value obtained by converting an AC voltage at the time of occurrence of an exciting rush current into a digital value of its instantaneous value.

In FIG. 27 (b), the instantaneous value at the current time is v _m , the instantaneous value one sample before (hereinafter, referred to as sp) is v _m−1 , the instantaneous value _two sp ago is v _m−2 , 3 sp ago Is the instantaneous value of v _m-3 ,...
Put _{m- (K-1)} .

[0353] To explain the amplitude value calculated at the instantaneous values of FIG. 27 (a), the of K instantaneous values of certain intervals during one cycle (e.g., of the section _{a v m ~v m- (K-} 1)) Is determined by the following equation (g). Note that the fixed section is not particularly limited as long as it is the same fixed section as the amplitude value calculating section 21.

[0354]

[Equation 68]

This value of Jv is referred to as an amplitude value, and represents an amplitude value in a certain section in one cycle of the AC voltage. When the current waveform in the certain section in one cycle of the differential current is flat, In addition, the amplitude value Jv becomes the largest value.

As in the case of the amplitude value J in the section a, calculation is performed using the past k sp numbers for each sp (in FIG. 27B, the sections b,
c) can always see the amplitude value in a certain section, and the individual amplitude values Jva, Jvb, Jvc... as shown in the calculation result in the amplitude value calculation unit 21 in FIG.
Value.

In the case where the differential current Id is generated by the exciting rush current having a flat section as shown in FIG. 27A, the value of the amplitude value Jv of the AC voltage is calculated as follows. When included in a flat part (section a in FIG. 27B)
The value is maximum. Further, when the amplitude value Jv is a constant value k
When a value larger than v is taken, the voltage value determination operation unit 42
Generates an output like the calculation result of the flatness determination calculation unit 42 in FIG.

The constant value kv is not particularly limited as long as it is a value for distinguishing the voltage value at the time of occurrence of an accident current from the voltage value at the time of occurrence of an inrush current. As a result, since the voltage value determination operation 42 generates an output at the same timing as the output of the flatness determination operation 22, the AND operation circuit 43 also generates an output at the same timing. Then, the output of the AND operation circuit 43 is made continuous by the return delay timer 23 having a delay time of about 1 cy or more, and the output of the excitation inrush current countermeasure element 71 is always sent out when the excitation inrush current occurs.

The output of the inrush current suppression element 71 is
Since the NOT operation circuit 19 inverts the output, the NOT operation circuit 19 does not always generate an output, and can always block the output of the logical product operation circuit 20. Therefore, the malfunction of the differential relay 80 with respect to the inrush current of the excitation. Can be prevented.

On the other hand, in the case of an internal fault in which harmonics that cause a transient flat portion in the fault current are generated, the terminal voltage of the transformer is greatly reduced. The output value of the amplitude value Jv is a predetermined value kv
And as a result, the voltage value determination operation 42 does not always produce an output. Therefore, the output of the flatness judgment operation unit 22 and the output of the voltage value judgment operation 42 are ANDed by the AND operation circuit 43, and the exciting inrush current countermeasure element 71 does not always generate an output.

The output of the excitation inrush current suppression element 71 is
Since the NOT operation circuit 19 inverts the output, the NOT operation circuit 19 always generates an output, and the differential relay 80 can operate normally without blocking the output of the AND operation circuit 20.

In the above description, the value representing the flatness has been described based on the amplitude value Jv, but may be a value represented by the following general formula (formula (g-1)). That is, among the computed differential current, digital amount of K instantaneous value of the electrical angle T of spacing _{(v m, v m-1} , v m-2, ..., v
_{m- (K-1)} ), and a value obtained by raising the amplitude value in a certain section to the Nth power is obtained. That is, N of the amplitude value represented by the equation (G-1)
The power Jv ^N is obtained as an amplitude value calculation.

[0363]

[Equation 69]

For example, when N = 2, (g-1)
The formula (g-2) may be used instead of the formula.

[Equation 70]

Then, the N-th power Jv of the obtained amplitude value is obtained.
By providing an excitation inrush current countermeasure element 71 having a voltage value determination operation unit 42 that generates an output when ^N is equal to or greater than a constant value kv, and by blocking the output of the differential element 5 with its output, A similar effect can be achieved. In the present embodiment, a voltage element is used for discriminating between an internal accident and an exciting rush current as in the case of the above-described claim 10. Therefore, this discrimination method is defined in claim 1
To claim 9.

As described above, in the present embodiment, the difference between the waveforms of the transformer inrush current and the transformer internal fault current, that is, the excitation inrush current is caused by the saturation of the magnetic flux of the transformer core during one cycle. While there is always a flat section where the current flows and the saturation of the transformer core is released and the current does not flow, the fault current has a flat section in the fixed section due to the fundamental current or the superposition of an unspecified number of harmonic currents. The difference between the voltage when the transformer inrush current occurs and the voltage when the transformer internal fault current occurs, that is, the voltage amplitude value is large when the magnetizing inrush current occurs, especially in the section where the magnetizing inrush current does not flow In addition, attention is paid to both the fact that the voltage amplitude value is small when an accident current occurs.

[0367] Then among the differential current Id, a digital quantity of the K instantaneous value of the electrical angle T of intervals _{(i m, i m-1} ,
_{i m-2, ..., i} m- (k-1), and v _m, v _m-1,
v _m−2 ,..., v _{m− (k−1)} ), and obtains a value obtained by multiplying the amplitude value of the current and the voltage in a certain section to the N-th power. And an excitation inrush current countermeasure element 71 that determines an excitation inrush current and generates an output when the two conditions that the voltage amplitude value is equal to or greater than a predetermined value kv are provided, and the flatness of the differential current Id, and The magnitude of the voltage value is detected.

The output of the differential element 5 is blocked by the output of the exciting rush current countermeasure element 71, so that the exciting rush current and the fault current can be reliably distinguished. It is difficult for the transformer Tr of the power system in which the internal fault current includes the harmonic current near the second harmonic to be surely inoperable by the transformer inrush current, and the internal fault current is difficult. A digital protection relay that can sometimes operate reliably can be obtained.

FIG. 28 is a functional block diagram showing a configuration example of a differential relay for protecting a transformer, which is a digital type protection relay according to claim 12, and the same parts as those in FIG. The description is omitted, and only different portions will be described here. That is, the differential relay 8 of the present embodiment
28, as shown in FIG. 28, the excitation inrush current countermeasure element 70 in the differential relay 80 of FIG. 24 is omitted, and a new excitation inrush current countermeasure element 72 is provided instead.

Further, the excitation inrush current countermeasure element 72 includes an amplitude value calculator 21, a flatness determination calculator 22, a return delay timer 23, a voltage rise determination calculator 44, a return delay timer 45, and a logical product calculation. And a circuit 46.
Here, the amplitude value calculation unit 21, the flatness determination calculation unit 22, and the return delay timer 23 have the same functions as in the embodiment of FIG. 26 described above.

Here, the voltage rise determination calculating section 44 detects whether the magnitude of the AC voltage v1 has risen by a certain value or more.
An output is generated when the voltage rises above a certain value. The return delay timer 45 is a return delay timer having a delay time longer than a time required for the exciting rush current to sufficiently attenuate below the operation level of the differential element. Further, the output of the return delay timer 23 and the output of the return delay timer 45 are ANDed by the AND operation circuit 46.

On the other hand, the output of the AND operation circuit 46 is set to NOT.
Inverted by the operation circuit 19,
By performing an AND operation with the output of the differential element 5 in
Blocking the output of the differential element 5 operating with the inrush current of the excitation,
A malfunction as the differential relay 80 is prevented.

Next, the operation of the differential relay 80 according to the present embodiment will be described. The operation of the differential element 5 is the same as that in the case of FIG. 31, and the description thereof is omitted here. In FIG. 28, the differential current Id derived by the differential current calculator 14 of the differential element 5 is introduced to the exciting rush current countermeasure element 72, and is calculated by the amplitude value calculator 21 to detect flatness. Is performed to obtain the amplitude value J.

When the amplitude value J obtained here is equal to or smaller than the predetermined value k, the flatness determination calculation section 22 generates an output.
Is continuous.

On the other hand, as in the case of the embodiment of FIG. 26, the voltage V1 at any one terminal of the transformer is converted into an appropriate voltage via a transformer PT, and The AC voltage V1 extracted by the PT is further converted to an appropriate magnitude by the input transformer 37,
It is introduced into the D converter 3. In the A / D converter 3,
The AC voltage V1 is sampled at regular time intervals and converted into a digital quantity v1.

[0376] The v1 converted into the digital quantity is introduced into the voltage rise determination calculation section 44. A known calculation algorithm may be used for the voltage rise determination calculation unit. For example, a difference value ΔV (ΔV = v (current) −v (one cycle before)) between the instantaneous value v (current) at the present time and the instantaneous value v (one cycle before) one cycle before is taken, and this difference is calculated. When the value ΔV is equal to or greater than the fixed value kv ′, the voltage rise determination calculation section 44 generates an output.

The output of the voltage rise determination calculation section 44 is
The return delay timer 45 is introduced into the return delay timer 45 and is delayed for return. The return delay timer 45 may be any one as long as it generates an output continuously for a period of time during which the exciting rush current attenuates and the differential element returns.

The return delay timer 45 is a return delay timer having a delay time longer than a time required for the exciting rush current to sufficiently attenuate below the operation level of the differential element. Further, the output of the return delay timer 23 and the output of the return delay timer 45 are ANDed by the AND operation circuit 46.

The output of the voltage rise determination calculation section 44 is
The logical product is ANDed with the output of the return delay timer 23 by the logical product arithmetic circuit 46, inverted by the NOT arithmetic circuit 19, and further performed by the logical product arithmetic circuit 20 with the output of the differential element 5. Thus, the output of the differential element 5 that operates by the inrush exciting current can be prevented, and malfunction as the differential relay 1 can be prevented.

Hereinafter, such a point will be described more specifically. The excitation inrush current has a periodicity between a period in which the current flows and a period in which the current does not flow, for each cycle due to the relationship of the transformer core saturation. For this reason, the output of the flatness determination operation unit 22 based on the inrush current is always sent once every cycle, and the output is an intermittent output having a periodicity every cycle, and a delay time of about one cycle or more. The output of the return delay timer 23 having the following is always transmitted.

When the transformer voltage is applied such that an exciting rush current is generated, the voltage is greatly increased as compared with before the transformer voltage is applied. Further, the output of the voltage rise determination calculation unit 44 is:
The return delay timer 45 is introduced to the return delay timer 45 and is delayed for return. The return delay timer 45 continuously generates an output for a time equal to or longer than the time when the exciting rush current is attenuated and the differential element returns.

The output of the return delay timer 23 and the output of the return delay timer 45 are ANDed by the AND operation circuit 46, so that the excitation inrush current countermeasure element 72
Generates at least an output from the time when the transformer voltage is applied until the differential element returns.

The output of the inrush current suppression element 72 is
Since the NOT operation circuit 19 inverts the output, the NOT operation circuit 19 does not always generate an output, and can always block the output of the logical product operation circuit 20. Therefore, the malfunction of the differential relay 80 with respect to the inrush current of the excitation. Can be prevented.

On the other hand, in the case of an internal accident, since the terminal voltage of the transformer always drops greatly, the voltage rise determination operation unit 44 does not always generate an output (since the condition of ΔV ≧ kv ′ is not satisfied). Further, the recovery delay timer 45 does not produce any output. Therefore, the output of the return delay timer 23 and the output of the return delay timer 45 are ANDed by the AND operation circuit 46, and the excitation inrush current countermeasure element 72 does not always output.

The output of the inrush current suppression element 72 is
Since the NOT operation circuit 19 inverts the output, the NOT operation circuit 19 always generates an output, and the differential relay 80 can operate normally without blocking the output of the AND operation circuit 20.

In the present embodiment, the degree of voltage rise is used to discriminate between an internal accident and an exciting rush current. That is, when a transformer voltage is applied, the voltage rises significantly as compared with before, and conversely, it drops when an internal accident occurs. Therefore, this determination method is described in claims 1 to
It applies to all of claim 11.

As described above, in the present embodiment, the difference between the waveforms of the transformer inrush current and the transformer internal fault current, that is, the excitation inrush current is caused by the magnetic flux saturation of the transformer core during one cycle. While there is always a flat section where the current flows and the saturation of the transformer core is released and the current does not flow, the fault current has a flat section in the fixed section due to the fundamental current or the superposition of an unspecified number of harmonic currents. And the voltage difference between when the transformer inrush current occurs and when the transformer internal fault current occurs, that is, the voltage rises significantly when the magnetizing inrush current occurs, and drops when the fault current occurs. This is the focus.

[0388] Then among the differential current Id, a digital quantity of the K instantaneous value of the electrical angle T of intervals _{(i m, i m-1} ,
i _m−2 ,..., _{im− (k−1)} ), and obtains a value obtained by multiplying the current and voltage amplitude values in a certain section to the Nth power, and this current amplitude value is not more than a predetermined value k. , And the voltage is a predetermined value k
An excitation inrush current countermeasure element 72 that determines an excitation inrush current and generates an output when the two conditions of increasing by at least v ′ are satisfied is provided to detect the flatness of the differential current Id and the magnitude of the voltage value. The output of the differential element 5 is blocked by the output of the exciting rush current countermeasure element 72.

As a result, the inrush current and the fault current can be reliably distinguished from each other, and the above-mentioned conventional power which is difficult to be applied is such that the internal fault current includes a harmonic current near the second harmonic. Even for the transformer Tr of the system, a digital protection relay can be obtained that can reliably operate when the transformer inrush current flows, and can operate reliably when an accident occurs inside the transformer.

FIG. 29 is a functional block diagram showing an example of the configuration of a differential relay for protecting a transformer, which is a digital protection relay according to claim 13, in which the same parts as those in FIG. The description is omitted, and only different portions will be described here. In addition, about the structure of the differential element 5,
Since the configuration is completely the same as that of FIG. 1, a part of the configuration is omitted in FIG.

That is, as shown in FIG. 29, the differential relay 1 according to the present embodiment outputs the output of the differential element 5 for one cycle between the differential element 5 and the AND operation circuit 20 in FIG. An operation delay timer 47 for delaying the time by about the same or more is newly provided, and an AND operation for calculating an AND of the output of the differential determination operation unit 16 of the differential element 5 and the return delay timer 23 of the exciting rush current countermeasure element 61 is provided. A circuit 48 is provided, and the output of the operation delay timer 47 is blocked by the output of the AND operation circuit 48.

The operation of the differential element 5 is described with reference to FIG.
Since this is the same as the case described above, the description is omitted here. In FIG. 29, the amplitude intrusion current countermeasure element 61 is introduced into the element 61, and the amplitude value calculation unit 21 performs the calculation based on the equation (A) described in the first embodiment, and calculates the differential current Id for each sp. The amplitude value J of a certain section in is calculated. Further, in the flatness determination calculation unit 22, the amplitude value J in a certain section is s.
The judgment calculation is always performed for each p.

However, since the differential current Id is usually zero in a state where a load current is flowing or a state where a passing current is flowing due to an external accident, the flat determination operation section 22 always operates to always make a determination. In this state, the output of the differential element 5 is always blocked.

If an internal accident occurs at this time, the output of the flatness determination calculation unit 22 is restored, but the operation time of the differential relay 1 is reduced by the excitation inrush current countermeasure element 61.
Is delayed by the time required to return the output of the return delay timer 23.

In this respect, in the present embodiment, a logical product operation of the output of the differential judgment calculation unit 16 and the exciting rush current countermeasure element 61 is performed by the logical product calculation circuit 48, and when the differential element 5 does not operate. Blocks the output of the excitation inrush current suppression element 61,
When the differential element 5 operates, the excitation inrush current suppression element 6
1 is allowed.

As a result, in the steady state where there is no differential current Id, unnecessary output blocking by the magnetizing inrush current countermeasure element 61 is not performed, and even if an internal accident occurs from this state, the operation of the differential relay 1 can be performed. The time delay can be reduced.

The operation delay timer 47 for delaying the output of the differential judgment operation section 16 cooperates with the exciting inrush current countermeasure element 61 activated by the output of the differential judgment operation section 16. This is for delaying the output of the differential judgment operation section 16 before the output of the excitation inrush current countermeasure element 61 when the inrush current occurs.

Thus, the output of the operation delay timer 47 for delaying the output of the differential element 5 is prevented by the operation output of the AND circuit 48 of the output of the differential element 5 and the output of the exciting rush current countermeasure element 61. This can prevent a malfunction as the differential relay 1.

In the case of an accident current having no flat section,
The output of the flatness determination calculation unit 22 does not occur, and the differential determination calculation unit 1
The output of the differential relay 1 is directly output from the differential relay 1 through the operation delay timer 47 and the logical product operation circuit 20, so that the normal operation can be performed. As is apparent from the above description, the determination method according to the present embodiment is applicable to all of claims 1 to 12.

As described above, in the present embodiment, the difference between the waveforms of the transformer inrush current and the transformer internal fault current, that is, the excitation inrush current is caused by the magnetic flux saturation of the transformer core during one cycle. While there is always a flat section where the current flows and the saturation of the transformer core is released and the current does not flow, the fault current has a flat section in the fixed section due to the fundamental current or the superposition of an unspecified number of harmonic currents. It is noted that it does not occur.

[0401] Then among the differential current Id, a digital quantity of the K instantaneous value of the electrical angle T of intervals _{(i m, i m-1} ,
i _m-2, ..., introduced _{i m- (k-1))} , determine the values of the amplitude value raised to the power N of the current and voltage at a predetermined interval, when the current amplitude value is equal to or less than a predetermined value k An inrush current countermeasure element 72 for determining an inrush current and generating an output is provided to detect the flatness of the differential current Id, and to provide a differential element between the differential element 5 and the logical product operation circuit 20. 5 is provided with an operation delay timer 47 for delaying the output of No. 5 for about one cycle or more,
Further, there is provided an AND operation circuit 48 for calculating an AND operation between the output of the differential judgment operation section 16 of the differential element 5 and the output of the return delay timer 23 of the exciting rush current countermeasure element 61. The output of the operation delay timer 47 is blocked by the output.

Therefore, regardless of the magnitude of the inrush current, the inrush current and the fault current can be reliably distinguished from each other. A transformer protection inrush with a transformer excitation inrush current, and a digital protection relay capable of operating reliably in the event of an internal transformer accident, even for a transformer Tr of a power system including harmonic currents of be able to.

The present invention is not limited to the above-described embodiments, and can be implemented in the same manner as in the following (a) to (e). (A) In each of the embodiments described above, the case where the transformer Tr is a two-winding transformer has been described as an example. However, the present invention is not limited to this.
The present invention can be similarly applied to a transformer protection differential relay having a plurality of terminals having three or more windings. (B) In the above-described tenth to twelfth embodiments, the AC voltage used may be the AC voltage of any terminal of the transformer, and is not particularly limited. For example, in a three-winding transformer, any of the primary terminal voltage, the secondary terminal voltage, and the tertiary terminal voltage may be used. (C) In the above-described tenth to twelfth embodiments, an example is described in which any one terminal voltage is used as the terminal voltage. However, the same applies when focusing on a plurality of voltages. Although not particularly shown, when attention is paid to a plurality of terminal voltages, for example, the output of the voltage value determination calculation unit as shown in FIG. 24 is used by AND. Such extensions are well known in the art and are, of course, within the scope of the present invention. (D) The sampling frequency of the A / D conversion is particularly limited to the above-mentioned value as long as it can distinguish the fault current and the inrush current by looking at the amplitude of the instantaneous value of the differential current. is not. (E) Equations (a) and (b) in each of the embodiments described above.
Equations (c), (d), and (e) calculate the amplitude value, and thus can be applied not only to the inrush current but also to the calculation of the amplitude value of normal current, voltage, and the like. The expression (g) in the eleventh embodiment is an example in which the expression (a) is applied as a voltage amplitude value calculation.

[0404]

As described above, according to the present invention, the difference between the waveforms of the transformer inrush current and the fault current inside the transformer, that is, the saturation of the transformer core in one cycle is caused by the inrush current of the transformer. Section where no current flows due to melting (no current period)
The fault current always exists, but the fault current does not have a current-free period due to the superposition of the fundamental current or unspecified harmonic current, and the flatness of the differential current is calculated by the amplitude value. In the past, it was difficult to apply by providing an exciting inrush current countermeasure element for determining an exciting inrush current when the value is equal to or less than a predetermined value, and by reliably distinguishing the exciting inrush current from the fault current. Even for transformers in power systems that include harmonic currents near the second harmonic in the internal fault current, the inrush current will surely disable operation, and can reliably operate in the event of a transformer internal fault. A digital protection relay can be provided.

[Brief description of the drawings]

FIG. 1 is a functional block diagram showing a first embodiment of a digital protection relay (differential relay) according to the present invention.

FIG. 2 is a waveform chart showing characteristics of a fault current waveform and an exciting inrush current waveform.

FIG. 3 is a view for explaining an operation in the first embodiment.

FIG. 4 is a view for explaining the operation in the first embodiment.

FIG. 5 is a functional block diagram showing a digital protection relay (differential relay) according to a second embodiment of the present invention.

FIG. 6 is a view for explaining the operation in the second embodiment.

FIG. 7 is a functional block diagram showing a digital protection relay (differential relay) according to a third embodiment of the present invention.

FIG. 8 is a diagram for explaining an operation in the third embodiment.

FIG. 9 is a functional block diagram showing a fourth embodiment of a digital protection relay (differential relay) according to the present invention.

FIG. 10 is a diagram for explaining an operation in the fourth embodiment.

FIG. 11 is a functional block diagram showing a fifth embodiment of a digital protection relay (differential relay) according to the present invention.

FIG. 12 is a view for explaining the operation in the fifth embodiment.

FIG. 13 is a functional block diagram showing a sixth embodiment of a digital protection relay (differential relay) according to the present invention.

FIG. 14 is a waveform diagram showing the characteristics of an exciting inrush current waveform when a transformer voltage is applied and an exciting inrush current waveform when an external accident is recovered, as seen from a digital protection relay (differential relay).

FIG. 15 is a view for explaining the operation in the sixth embodiment.

FIG. 16 is a view for explaining an operation in the sixth embodiment.

FIG. 17 is a functional block diagram showing a seventh embodiment of a digital protection relay (differential relay) according to the present invention.

FIG. 18 is a view for explaining the operation in the seventh embodiment.

FIG. 19 is a functional block diagram showing an eighth embodiment of a digital protection relay (differential relay) according to the present invention.

FIG. 20 is a view for explaining the operation in the eighth embodiment.

FIG. 21 is a view for explaining the operation in the eighth embodiment.

FIG. 22 is a functional block diagram showing a ninth embodiment of a digital protection relay (differential relay) according to the present invention.

FIG. 23 is a view for explaining the operation in the ninth embodiment;

FIG. 24 is a functional block diagram showing a tenth embodiment of a digital protection relay (differential relay) according to the present invention.

FIG. 25 is a circuit diagram showing an example in which a differential relay is applied to a transformer.

FIG. 26 is a functional block diagram showing an eleventh embodiment of the digital protection relay (differential relay) according to the present invention.

FIG. 27 is a view for explaining the operation in the eleventh embodiment.

FIG. 28 is a functional block diagram showing a twelfth embodiment of a digital protection relay (differential relay) according to the present invention.

FIG. 29 is a functional block diagram showing a thirteenth embodiment of a digital protection relay (differential relay) according to the present invention.

FIG. 30 is a circuit diagram showing an example in which a differential relay is applied to a transformer.

FIG. 31 is a functional block diagram showing a configuration example of a conventional differential relay.

[Explanation of symbols]

G Power system power supply CB breaker CT1, CT2 Current transformer (CT) Tr Transformer PT Transformer for instrument PT 1, 80 Differential relay 2 Transformer (CT) 3 A / D converter 4 CPU 5 Differential element 6 Exciting inrush current countermeasure element (2f detection) 11, 12 Amplitude value calculation unit 13 Suppression current (scalar sum) calculation unit 14 Differential current (vector sum) calculation unit 15 Amplitude value calculation unit (1f) 16 Differential judgment calculation unit 17 Amplitude value calculation unit (2f) 18 2f determination calculation unit 19 NOT (inversion) calculation circuit 20, 33, 40, 43, 46, 48 Logical product (AN
D) Operation circuit 21, 24, 25, 26, 27, 28, 41 Amplitude value operation unit 22, 29, 36 Flatness judgment operation unit 23, 45 Return delay timer 30 Logical OR (OR) operation circuit 31, 47 Operation delay timer 32, 34 shift operation unit 35 maximum value detection operation unit 37 transformer (PT) 38 voltage amplitude value operation unit 39, 42 voltage value judgment operation unit 44 voltage rise judgment operation unit 61-72 excitation inrush current suppression element

[Equation 71]

 ──────────────────────────────────────────────────続 き Continued on the front page (72) Inventor Hiroshi Yamakawa 1-3-1 Uchisaiwai-cho, Chiyoda-ku, Tokyo Tokyo Electric Power Company (72) Inventor Mitsuru Yamaura 1-Toshiba-cho, Fuchu-shi, Tokyo Toshiba Fuchu, Inc. Inside the factory (72) Inventor Satoshi Nakano 1 Toshiba-cho, Fuchu-shi, Tokyo Inside the Fuchu factory, Toshiba Corporation (72) Inventor Rikio Sato 1-toshiba-cho, Toshiba-cho, Fuchu-shi, Tokyo Inside the Fuchu factory, Toshiba (72) Inventor Masao Hori 1-1-1, Shibaura, Minato-ku, Tokyo Inside the Toshiba head office

Claims (13)

[Claims] 1. An alternating current for each phase is introduced across a protected object having a plurality of terminals, and the introduced alternating current is sampled at fixed time intervals to obtain a digital amount of an instantaneous value of the alternating current. Converted, a differential current for each phase is obtained using the converted digital amount, and when the amount of electricity based on the obtained differential current is equal to or greater than a predetermined value, it is determined that an internal accident has occurred and the output is determined. in the first judging means digital protection relay with differential protection element having caused, among the determined differential current, digital amount of K instantaneous value of the electrical angle T of intervals (i _m, i _m-1 , im _-2 , im _-3 ,
.., _{Im- (K-1)} ), and the amplitude value in a constant section of the differential current is calculated by the following amplitude value calculation equation (a). A second judging means for judging whether or not the output is equal to or less than a predetermined value, and an exciting rush current countermeasure element having first return delay means for delaying the output of the second judging means for a predetermined time, A digital protection relay, wherein the output of the differential protection element is blocked by the output of the excitation inrush current suppression element. (Equation 1) 2. An alternating current for each phase is introduced across a protected object having a plurality of terminals, and the introduced alternating current is sampled at regular time intervals to obtain a digital amount of an instantaneous value of the alternating current. Converted, a differential current for each phase is obtained using the converted digital amount, and when the amount of electricity based on the obtained differential current is equal to or greater than a predetermined value, it is determined that an internal accident has occurred and the output is determined. in the first judging means digital protection relay with differential protection element having caused, among the determined differential current, digital amount of three instantaneous value of the electrical angle T of intervals (i _m, i _m-1 and im _-2 ), the amplitude value of the differential current in a certain section is calculated by the following amplitude value calculation formula (b), and whether or not the obtained amplitude value is equal to or less than the certain value is determined. And outputs when the value is below a certain value.
And an inrush current suppression element having second return delay means for delaying the output of the third determination means by a predetermined time. The differential protection element is provided by the output of the inrush current suppression element. A digital protection relay characterized by blocking the output of the digital protection relay. (Equation 2) 3. An alternating current for each phase is introduced across a protected object having a plurality of terminals, and the introduced alternating current is sampled at regular time intervals to obtain a digital amount of an instantaneous value of the alternating current. Convert, determine the differential current for each phase using the converted digital quantity, and when the electrical quantity based on the determined differential current is equal to or greater than a predetermined value, determine that an internal accident has occurred and generate an output. in the digital protective relay provided with a differential protection element having a first determination means, among the determined differential current, digital amount of four instantaneous value of the electrical angle T of intervals (i _m, i _{m -1} , im _-2 , im _-3 ), and the amplitude value in a constant section of the differential current is calculated by the following amplitude value calculation formula (c), and the amplitude value obtained here is a fixed value. A fourth determining means for determining whether or not the value is equal to or less than a predetermined value and outputting the result when the value is equal to or less than a certain value; And an exciting inrush current countermeasure element having third return delay means for delaying the output of the fourth determination means by a predetermined time. The output of the exciting inrush current countermeasure element prevents the output of the differential protection element. A digital protection relay characterized in that: (Equation 3) 4. An alternating current for each phase is introduced across an object to be protected having a plurality of terminals, and the introduced alternating current is sampled at fixed time intervals to obtain a digital amount of an instantaneous value of the alternating current. Convert, determine the differential current for each phase using the converted digital quantity, and when the electrical quantity based on the determined differential current is equal to or greater than a predetermined value, determine that an internal accident has occurred and generate an output. in the digital protective relay provided with a differential protection element having a first determination means, among the determined differential current, digital amount of five instantaneous value of the electrical angle T of intervals (i _m, i _{m -1} , im _-2 , im _-3 , i
_m-4 ) is introduced, the amplitude value of the differential current in a certain section is obtained by the following amplitude value calculation formula (d), and it is determined whether or not the obtained amplitude value is equal to or less than the certain value, and the constant value is determined. A fifth determining means for outputting when the value is equal to or less than a value, and an exciting rush current countermeasure element having fourth return delay means for returning and delaying the output of the fifth determining means for a predetermined time. A digital protection relay, wherein an output of the differential protection element is blocked by an output. (Equation 4) 5. An alternating current for each phase is introduced across a protected object having a plurality of terminals, and the introduced alternating current is sampled at regular time intervals to obtain a digital amount of an instantaneous value of the alternating current. Convert, determine the differential current for each phase using the converted digital quantity, and when the electrical quantity based on the determined differential current is equal to or greater than a predetermined value, determine that an internal accident has occurred and generate an output. in the digital protective relay provided with a differential protection element having a first determination means, among the determined differential current, digital amount of six instantaneous value of the electrical angle T of intervals (i _m, i _{m -1} , im _-2 , im _-3 , i
_m-4 , im _-5 ), and the amplitude value in a constant section of the differential current is calculated by the following amplitude value calculation equation (e), and whether or not the calculated amplitude value is equal to or less than the certain value is determined. And a sixth return means for returning the output of the sixth determiner for a predetermined period of time. A digital protection relay, wherein the output of the differential protection element is blocked by the output of an inrush current countermeasure element. (Equation 5) 6. The digital protection relay according to claim 1, wherein said digital current comprises:
The same or a different electrical angle T and the electrical angle T digital amount 'of degree intervals, the same or a different K and the number K' pieces of instantaneous value _{(i m ', i m-} 1', i m-2 ' ,
im ₋₃ ′,..., _{im− (K′−1)} ′), and the amplitude value in a constant section of the differential current is calculated by the following amplitude value calculation formula (f). A seventh determining means for determining whether the amplitude value is equal to or less than a certain value and outputting when the amplitude value is equal to or less than the certain value;
A first logical sum calculating means for calculating a logical sum of an output of the seventh determining means and an output of the second to sixth determining means is newly added to the element for preventing an inrush current A digital protection relay characterized by the following. (Equation 6) 7. The digital protection relay according to claim 1, wherein the first operation delay means for delaying the output of the second determination means to the sixth determination means for a predetermined time is a measure against the inrush current. A digital type protection relay, wherein an output of the first operation delay unit is newly added to an element, and an output of the first operation delay unit is used as an input of the first return delay unit to the fifth return delay unit. 8. The digital protection relay according to claim 1, wherein the current output of the second judging means to the sixth judging means and one cycle of the second judging means to the sixth judging means. Alternatively, a first AND operation means for performing an AND operation with the output of a plurality of cycles before is newly added, and the output of the first AND operation means is output from the first return delay means to the fifth return delay. A digital protection relay characterized in that the input is means input. 9. The digital protection relay according to claim 1, wherein a current value of the obtained amplitude value is compared with a value one cycle or a plurality of cycles ago or a value one sample before. Eighth determination means for obtaining a larger value, determining whether the larger value is equal to or smaller than a predetermined value, and generating an output when the larger value is equal to or smaller than the predetermined value, is newly added. A digital protection relay, wherein an output of the means is used as an input of the first to fifth recovery delay means. 10. The digital protection relay according to claim 1, wherein an AC voltage for each phase of any one of the terminals to be protected having a plurality of terminals or the plurality of terminals is introduced. The obtained AC voltage is sampled at fixed time intervals, and converted into a digital value of the instantaneous value of the AC voltage.The converted digital value is used to obtain the amplitude value of the voltage for each phase. Ninth determining means for generating an output when the amplitude value of the voltage is equal to or greater than a predetermined value, and a logic of an output of the ninth determining means and an output of the second to fifth recovery delay means. A digital protection relay, wherein a second logical product calculating means for calculating a product is newly added to the element for preventing an inrush current. 11. The digital protection relay according to claim 1, wherein an AC voltage for each phase of any one terminal or a plurality of terminals of the protected object having a plurality of terminals is introduced. Each of the obtained AC voltages is sampled at regular time intervals and converted into a digital quantity of an instantaneous value of the AC voltage. Of the obtained AC voltages, a digital quantity (V) of K instantaneous values at an electrical angle T degree interval is obtained. _m , V _m-1 , V
_m−2 , V _m−3 ,..., V _{m− (K−1)} ), and the amplitude value in a constant section of the AC voltage is calculated by the following amplitude value calculation formula (g). A tenth judging means for judging whether or not the obtained amplitude value is equal to or more than a certain value, and outputting the result when the amplitude value is not less than the certain value; 3. A digital protection relay according to claim 1, wherein a third logical product calculating means for calculating a logical product with an output of said means is newly added to said exciting rush current countermeasure element. (Equation 7) 12. The digital protective relay according to claim 1, wherein an AC voltage for each phase of any one terminal or a plurality of terminals of the object to be protected having a plurality of terminals is introduced. The obtained AC voltage is sampled at fixed time intervals, converted into a digital value of the instantaneous value of the AC voltage, and the amplitude value of the voltage for each phase is obtained using the converted digital value. An eleventh determining means for generating an output when the amplitude value of the first determining means increases by a predetermined value or more, a sixth returning delay means for delaying the output of the eleventh determining means for a predetermined time, and the sixth returning delay means And a fourth AND operation means for calculating the AND of the output of the first and second elements and the excitation inrush current countermeasure element is newly added.
A digital protection relay, wherein the output of the differential protection element is blocked by the output of the AND operation means. 13. The digital protection relay according to claim 1, wherein second operation delay means for operating the output of the differential protection element for a predetermined time, and outputting and exciting the differential protection element. Fifth logical product calculating means for calculating logical product with the output of the inrush current countermeasure element is newly added,
A digital protection relay, wherein an output of said second operation delay means is blocked by an output of said fifth AND operation means.