JPH0456534B2 - - Google Patents

Description

[Detailed Description of the Invention] [Field of Application of the Invention] The present invention relates to a transformer protective relay device, which is particularly capable of preventing malfunctions caused by magnetizing inrush current of a transformer, and which selectively detects only internal failures and operates the device. The present invention relates to a transformer protection relay device characterized by:

[Background of the invention]

Conventionally, transformer protection in the event of an abnormality such as a winding failure in a transformer is achieved by extracting the current passing through each terminal of the protected transformer as an equivalent current signal corresponding to the transformation ratio using a current transformer, In many cases, current differential or current ratio differential is performed based on this.

However, in the current differential or current ratio differential system, differential current is generated when there is an internal failure in the transformer.
Differential currents are also generated by so-called magnetizing inrush currents that occur when a transformer is excited with no load or when the voltage is restored when an external fault is removed. Conventionally, therefore, malfunctions caused by the magnetizing inrush current have been prevented by focusing on the specificity of the magnetizing inrush current waveform.

One method is to
Taking advantage of the fact that the proportion of high frequency components is higher than that in the fault current, when the proportion of the second high frequency component in the differential current is above a certain value, it is determined to be a magnetizing inrush current and the breaker is triggered. The removal command is not output.

However, in recent years, as power transmission systems have become larger in capacity and longer distances, and cable systems have expanded, the ground capacitance of power transmission systems has increased, and the resonance frequency with the system inductance has tended to decrease. It is predicted that a large amount of low-order harmonic current near the second high frequency will be generated due to system fluctuations when an internal failure occurs. If the second harmonic component in the internal fault current increases in this way, the conventional method described above will delay the operation of the transformer protective relay device, which can lead to serious disasters such as destruction of the transformer tank due to malfunction. There is a risk of inviting

Another method for preventing malfunctions of transformer protective relay devices due to magnetizing inrush current is to combine both, focusing on the fact that the fault current is a full-wave current, but the magnetizing inrush current is a half-wave current with discontinuities in the waveform. There is something to be identified (Japanese Patent Application Laid-open No. 153142-1983). An example of this prior art is shown in FIG. 1, and will be explained below.

In Figure 1, 1 is the transformer to be protected, 21, 2
2 is a current transformer inserted into the primary side and the secondary side of this transformer, 23 and 24 are current transformers inserted into the secondary side of current transformers 21 and 22, 25 is a current transformer 23, 24 is a current transformer inserted into a differentially connected circuit for deriving a differential current; 3 is a current transformer 23, 24, 25;
41 is a rectangular wave conversion circuit that generates an output signal when the absolute value of the differential current that is the output of the current transformer 25 exceeds a predetermined detection level; Invert the input signal and output it
NOT circuit, 43 is a fixed time limit for the rise of the input signal
44 is a time limit circuit that delays the input signal by T ₁ and outputs the output; 44 is a time limit circuit that holds the input signal for a certain period of time T ₂ ;
is an instantaneous relay element that operates instantaneously when the differential current that is the output of the current transformer 25 exceeds a certain value. Reference numeral 61 designates an inhibit circuit, the output of the time limit circuit 44 is input to the inhibit terminal, and the output of the ratio differential relay element 3 is input to the other terminal. 62 is an OR circuit to which the outputs of the inhibit circuit 61 and the instantaneous relay element 5 are input, and outputs a trip signal.

The operation with respect to the excitation inrush current in the example of the prior art shown in FIG. 1 will be explained with reference to FIG. 2. In the case of excitation inrush, the differential current ΣI has a half-wave waveform as shown in the figure. After the differential current ΣI exceeds the predetermined detection level ε, the ratio differential relay element 3 is activated and produces an output signal (Out3). While ΣI exceeds a predetermined detection level ε, the rectangular wave conversion circuit 41 outputs a signal (Out 41), and this signal is inverted by the NOT circuit 42. That is, the NOT circuit 42 generates an output signal while the differential current ΣI is smaller than the predetermined detection level ε (Out 42). Next, the timer circuit 43 delays the rise of the signal at Out42 by a fixed time period _T1 (approximately 60 degrees in electrical angle) (Out43). The time limit T ₁ is the differential current ΣI
Out 43 is still producing a signal approximately every cycle since the time during which is less than the detection level ε. As a result of being held for a certain period of time T ₂ (about one cycle) by the time limit circuit 44, a continuous output signal is generated (Out 44). Therefore, the inhibit circuit 61 does not output a signal (Out 61) and the circuit breaker is not tripped.

Next, the operation with respect to an internal fault current in the conventional example shown in FIG. 1 will be explained with reference to FIG. The symbols of each signal in FIG. 3 are the same as in FIG. 2. What is different from the case of excitation inrush current in Figure 2 is that the differential current ΣI
is a full-wave waveform, and the period during which ΣI is smaller than a predetermined detection level is short. Therefore, the output (Out42) of the NOT circuit 42 becomes a narrow signal as shown in the figure, and as a result of delaying the rise of the signal by a fixed time period _T1 , the signal at Out43 becomes zero continuously. Therefore, the signal is held for a certain period of time T ₂
Out44 becomes T ₂ after the signal of Out43 becomes zero.
It becomes zero after some time. Therefore, the inhibit condition with the output signal Out3 of the ratio differential relay element 3 is established,
An output signal is generated in the inhibit circuit 61 (Out6
1) A breaker trip signal is output.

As described above, when the differential current at the time of an internal failure has a sinusoidal full-wave waveform, the conventional technique shown in FIG. 1 operates normally. However, as described above, as the ground capacitance of the power transmission system increases, there are cases in which the power transmission system cannot operate normally when harmonic current is generated in the event of an internal failure. This will be explained with reference to FIG.

Figure 4 shows the conventional differential current ΣI shown in Figure 1 when an internal fault occurs, when a harmonic component is superimposed on the fundamental wave component shown by the dashed line, resulting in a distorted waveform as shown by the solid line. It shows how the technology works. Each signal is the same as in FIGS. 2 and 3. The difference from the sinusoidal full-wave waveform shown in FIG. 3 is that there are many random periods in which the absolute value of the differential current ΣI is smaller than the detection level ε.
Out 42 is also a signal corresponding to this. As a result, as shown in the figure, when the rise of the signal at Out42 is delayed by a fixed time period _T1 ,
After the signal once becomes zero, the next signal may have already started to be output, and the signal is output to Out 43 when the delay of the fixed time period _T1 ends.
The signal of Out43 is generated randomly, and for a certain period of time T ₂
As a result of holding the output, Out44 becomes a continuous signal, and the output Out61 of the inhibit circuit 61 does not generate a signal or is tripped. This situation continues until the harmonics of the differential current ΣI are attenuated, which may lead to a delay in the operation of the transformer protective relay device, and even a malfunction that may lead to a serious disaster.

[Purpose of the invention]

The purpose of the present invention is to eliminate the drawbacks of the above-mentioned conventional technology, detect internal failures of transformers with high sensitivity, and provide a highly reliable transformer protection relay device that prevents malfunctions caused by magnetizing inrush current with a simple configuration. Our goal is to provide the following.

[Summary of the invention]

In order to achieve the above object, in the present invention, in particular, in a digital method in which current is sampled at appropriate time intervals, one sampled current value is used to determine whether or not there is a discontinuity in the differential current ΣI. Instead, it is configured to use a plurality of continuous current values.

[Embodiments of the invention]

Hereinafter, the configuration of an embodiment of the present invention will be explained with reference to FIG. In FIG. 5, the same parts as in FIG. 1 are designated by the same reference numerals as in FIG. 1, and explanations thereof will be omitted. In FIG. 5, reference numeral 3 denotes a first relay element that detects the differential current of the terminal currents of each winding of the protected transformer 1 and outputs a breaker tripping command. It is a relay element. 7 samples and captures the differential current at appropriate time intervals to determine whether it is an internal failure or excitation inrush current, and when it is determined that it is an internal failure, outputs a signal that allows the output of the above-mentioned disconnector trip command. In the second relay element, the level determination section 71
and a time determination section 72. Each time the differential current ΣI is sampled, the level determination unit 71 determines whether or not the latest consecutive sampling values exceed a predetermined detection level ε. When one absolute value exceeds the detection level ε, it is determined that the level is high and "1" is output; otherwise, it is determined that the level is low and "0" is output. The time determination unit 72 determines the duration of time during which the output signal of the level determination unit 71 is “1”, and when the duration exceeds a predetermined determination time, that is, the output signal of the level determination unit 71 is “1”. ”, but when this state continues for a predetermined number of sampling times, it is determined that there is an internal failure and a signal “1” is output. If this is not the case, it is determined that excitation inrush has occurred and a signal "0" is output.
81 is an AND circuit, which connects the first relay element 3 and the second relay element 3;
The output signal of the relay element 7 is inputted, and when the AND condition is satisfied, a disconnection trip command is output.

The feature of the present invention lies in the configuration of the second relay element 7 which is a digital system, and the above-mentioned level determination, time determination, etc. are performed using a microcomputer or the like. FIG. 6 shows an example of a specific arithmetic processing flow for each sampling of the differential current ΣI in the second relay element 7 in this case.

In Fig. 6, the calculation processing of Step 1 to Step 4 is as follows:
The operation of the level determination section 71 in FIG. 5 corresponds to the operation of the time determination section 72 in FIG. 5, and the calculation processing in Steps 5 to 8 corresponds to the operation of the time determination section 72 in FIG. In the calculation processing flow example shown in Figure 6, the level is determined using six consecutive sampling values, and the high level is 25.
If this occurs continuously, it is determined that there is an internal failure. Although it is clear that the operations of level determination and time determination in the second relay element 7 described above are realized by the arithmetic processing contents shown in FIG. 6, some explanation will be added below.

The differential current storage area stores six sampling values of the differential current ΣI, and the latest sampling value of Σ1 sampled in Step 1 is
In Step 2, it is replaced with the oldest sampling of ΣI. In Step 3, it is determined whether each of the latest six sampling values stored in the differential current storage area is larger than a predetermined detection level ε, and the absolute value of at least one sampling value is ε. If it is larger, it is determined to be a high level and the process proceeds to Step 4'; otherwise, when the absolute values of the six sampling values are all smaller than the detection level ε, it is determined to be a low level and the process proceeds to Step 4.

The time counter is initially set to "25", and when it is at a high level, that is, when the output Out71 of the level determination section 71 is determined to be "1" in Step 5, it is subtracted by "1" in Step 6', and when it is at a low level. In other words, when Out71 is determined to be “0” in Step 5, “25” is determined in Step 6.
will be reset to In Step 7, it is determined whether or not the time counter has become “0” or less, and when it is “0” or less, that is, when the high level continues for 25 times or more.
Proceeding to Step 8', "1" is output as the output Out72. When the time counter is greater than “0”
Proceed to Step 8 and output "0" as Out72.

Next, a specific example of the arithmetic processing shown in FIG. 6 in the second relay element 7 according to the present invention will be explained with reference to FIG. 7 for the case of excitation inrush current. FIG. 7 shows an example in which sampling of the differential current ΣI is performed at intervals of 15 degrees in electrical angle, and the sampling points are indicated by black circles in the figure. The numbers in the figure are the values of the time counter in the time determination section 72. It is clear from the above explanation of the arithmetic processing contents that the signal of the output Out71 of the level determination section 71 becomes "1" from the time when the differential current ΣI first exceeds the predetermined detection level ε, and the six sampling values of ΣI are When all of them become smaller than the detection level ε, they return to "0".
While Out71 is “1”, the value of the time counter is greater than “0”, and the output of the time determination unit 72
Out72 remains at "0". Therefore, the AND circuit 81 in FIG. 5 does not output a chopstick or disconnection trip command.

A specific example of the arithmetic processing shown in FIG. 6 in the second relay element 7 according to the present invention when the differential current has a sinusoidal full-wave waveform due to an internal failure will be described with reference to FIG. 8. When the absolute value of the differential current ΣI first exceeds the predetermined detection level ε, the signal of the output Out71 of the level determination section 71 becomes "1".
After that, there are times when the sampling value of ΣI becomes smaller than the detection level ε, but all six consecutive sampling values never become smaller than the detection level ε, and Out71 becomes a continuous “1” signal.
At the instant when the time counter reaches "0" after approximately one cycle, the signal at the output Out72 of the time determining section 72 changes from "0" to "1". Since the first relay element 3, which is a ratio differential relay element in FIG. 5, continues to output the signal "1" after the differential current ΣI exceeds the detection level ε, Out72 becomes "1". The AND condition is satisfied at the moment the AND circuit 81 outputs a mustard breaker trip command.

Next, a specific example of the arithmetic processing shown in FIG. 6 in the second relay element 7 according to the present invention when the differential current includes a harmonic component due to an internal failure will be described with reference to FIG. 9. The waveform of the differential current ΣI in FIG. 9 is the same as that in FIG. 4 used in the explanation of the prior art, and periods in which the absolute value of ΣI is smaller than the detection level ε occur many times at random. Even in such a case, all six consecutive sampling values will not be smaller than the detection level ε, and the eighth
Similarly to the case shown in the figure, when the time counter reaches "0", the output Out72 of the time determining section 72 changes from "0" to "1", and the AND circuit 81 outputs a shiya breaker trip command.

In the above description of one embodiment of the present invention, a case has been shown in which the differential current ΣI is sampled at 15° intervals and whether the differential current ΣI is high level or low level is determined based on six consecutive sampling values. When the sampling time interval of the differential current ΣI is expressed as Δθ (degrees) in electrical angle, and the level is determined using N consecutive sampling values, the level must be determined within the determination period θ _A shown in equation (1). Become.

θ _A = Δθ・(N-1) (degrees) ...(1) Minimum value of the period during which the differential current ΣI is smaller than the detection level ε (referred to as the zero pause period) between the half-wave waveforms of the magnetizing inrush current When is θ _O min, in order to correctly determine the excitation inrush current in the present invention, the determination period θ _A must be set smaller than θ _O min. Furthermore, the setting is made so that the condition of equation (2) is satisfied, taking into account the deviation of one sampling time.

θ _A ≦θ _O min−Δθ (2) From equations (1) and (2), the number of samples N required for level determination is set so as to satisfy the condition of equation (3).

N≦θ _o min/Δθ (3) In order to further clarify the sampling number N necessary for level determination, the minimum value θ _o min of the zero pause period of the excitation inrush current will be explained next.

Figure 10 shows how a transformer's excitation inrush current is generated. In FIG. 10, e is the power supply voltage applied to the transformer, B is the transformer core magnetic flux density, and Io is the exciting current of the transformer. In the waveform of the magnetic flux density B, B _n indicates the rated magnetic flux density, B _S indicates the saturation magnetic flux density, and B _R indicates the residual magnetic flux density. The first condition is that the excitation inrush current is maximum and the zero pause interval of the excitation inrush current is minimum.
In Figure 0, the residual magnetic flux density B _R is a positive value, and the power supply voltage e
This shows the case where the phase is 0° and the power is turned on. In the figure,
The broken line indicates the case where there is no attenuation, but in reality it becomes like the solid line due to the attenuation effect due to the resistance of the circuit.

Let us find the zero pause period θ _O of the magnetizing inrush current when there is no attenuation. When the power supply voltage e is set as e=E _n sinωt (4), the magnetic flux density B indicated by the broken line in FIG. 10 can be expressed by equation (5).

B=B _n +B _R +B _n sin(ωt−π/2) …(5) Since B=B _S when ωt=θ _O /2, B _S =B _n +B _R +B _n sin(θ _O /2 −π/2) …(6) Transform equation (6) to obtain equation (7).

θ _O = π−2sin ^-1 {B _n +B _R −B _S /B _n } …(7) Therefore, the zero pause period θ _O is the rated magnetic flux density B _n of the transformer core, the residual magnetic flux density B _R , and the saturation magnetic flux. It depends on the value of density B _S.

Therefore, B _S is set to 2.02 (T), and the value of θ _O when B _n and B _R are different is determined. The results are shown in FIG. The zero pause period θ _O is expressed in electrical angle (degrees). Generally, the rated magnetic flux density B _n of a transformer is approximately
1.7 (T), and the maximum value of the residual magnetic flux density B _R is about 0.82 (P·u) of the rated magnetic flux density. Therefore, from Fig. 11, the zero pause period θ _O in the excitation inrush current is approximately
Greater than 100 (degrees). B _n is 1.8 (T), B _R is rated
Even in the case of 0.9 (P·u), θ _O is larger than about 75°. Considering the attenuation of the excitation inrush current, the detection level ε, etc., the zero pause period θ _O becomes a larger value.

Therefore, for example, the minimum zero pause period of the excitation inrush current is θ _O min = 100°, and the sampling time interval is Δθ =
Assuming that the angle is 15°, the number of samples N required for level determination is as follows from equation (3): N≦6 (8).

In this case, the judgment period θ _A for determining the level from equation (1)
is θ _A ≦75 (degrees) …(9).

On the other hand, in the case of an internal fault, the smaller the fault current value, the longer the zero pause period during which the differential current ΣI is smaller than the detection level ε. Therefore, in order to detect internal failures with high sensitivity, the larger the values of N and θ _A are, the better. Therefore, in one embodiment of the present invention described above, N
The case where the maximum value of equation (8) is used as the value of is shown.
Note that if the differential current ΣI at the time of an internal failure includes a DC component, the zero pause period may become long, so even if the differential value of the differential current ΣI is used to remove the influence of the DC component. good. Even in this case, the zero pause period of the magnetizing inrush current remains unchanged.

In the embodiment of the present invention described above, a plurality of consecutive (for example, six) differential currents ΣI are used for level determination.
If the absolute value of even one of the sampled values exceeds the detection level ε, it is determined to be a high level, and if all of them are smaller than ε, it is determined to be a low level.

For example, out of multiple (for example 7) sampling values, two or more absolute values are at the detection level ε.
It may be determined that if it exceeds ε, it is determined to be a high level, and if there is one or less that exceeds ε, it is determined to be a low level. Such a method is considered to be effective in preventing erroneous determinations due to noise.

The content of FIG. 6, which is shown as an example of the arithmetic processing flow of the second relay element 7 of the present invention, can be modified in various ways.

For example, in FIG. 6, the process of Step 5 can be deleted, and Step 4 can proceed directly to Step 6, and Step 4' can proceed directly to Step 6'. However, in this case, the distinction between the level judgment section 71 and the time judgment section 72 in FIG. 5 becomes unclear, but in the digital system, originally, individual functions such as level judgment and time judgment exist independently. In order to perform efficient arithmetic processing as a whole, it is normal for the arithmetic processing flow to be a mixture of various functions. Furthermore, in Figure 6,
It is also possible to delete the processing in Step 4 and Step 4'.

In addition, FIGS. 5 and 6 in the present invention indicate that ``When the high level continues for a predetermined number of sampling times (for example, 25 times), it is determined that there is an internal failure and a signal is output that allows the output of the shield breaker trip command. However, he explained, ``When the level is low, it is judged as excitation inrush,
In other words, it outputs a signal that prevents the output of the disconnection trip command only after a predetermined sampling number (for example, 25 times). The arithmetic processing flows for both are exactly the same. In this case, the AND circuit 18 in FIG. 5 is replaced with an inhibit circuit,
The output of the second relay element 7 is input to the inhibit terminal side, and in Step 8 in FIG.
Instead of outputting “0”, output “1”,
Instead of outputting "1" in Step 8', "0" may be output. In this way, the concept of detecting the excitation inrush current and blocking the output of the shingle breaker trip command becomes clear.

In the present invention, approximately one cycle is required from when an internal failure occurs until a mustard disconnection trip command is output. Next, a means for shortening this time will be explained.

Generally, the differential current ΣI at the time of an internal failure has a double waveform, and can take both positive and negative polarity values in one cycle. Moreover, the polarity changes almost instantly from positive to negative, or from negative to positive. Even when the detection level ε is considered, the time from when the detection level ε is exceeded with positive polarity until it exceeds ε with negative polarity, for example, is shorter than the zero pause period in the excitation inrush current described above. On the other hand, the excitation inrush current always has a half wave waveform. Therefore, within a certain period of time, the differential current ΣI
By determining that there is an internal failure when the voltage exceeds the detection level ε for both positive and negative polarities, the breaker trip command can be output in less than one cycle.

As a specific example, the calculation processing flow example in Figure 6 is
In Step 3, the process of determining whether "at least one of the six sampled values in the differential current storage area has positive polarity and exceeds the detection level, and at least one has negative polarity and exceeds the detection level" is added, and when this condition is satisfied, other arithmetic processing is skipped and the process proceeds to Step 8'. Or the 6th
Such a determination process may be performed separately from the calculation process shown in the figure.

〔Effect of the invention〕

As detailed above, according to the present invention, malfunctions caused by magnetizing inrush current can be reliably prevented with a simple configuration, and
Since internal failures can be detected with high sensitivity, it can greatly contribute to increasing the reliability of transformer protective relay devices and preventing the spread of internal failures into serious disasters.

[Brief explanation of the drawing]

Fig. 1 is a schematic diagram for explaining the configuration of the prior art, Figs. 2 to 4 are time charts for explaining the operation of the prior art, and Fig. 5 shows the configuration of the embodiment of the present invention. 6 is a calculation flow for explaining the functions of the present invention, FIGS. 7 to 9 are time charts for explaining the operation of the present invention,
FIG. 10 is a time chart for explaining the excitation inrush current, and FIG. 11 is its characteristic diagram. 1...Transformer to be protected, 21-25...Current transformer, 3
...first relay element, 7...second relay element, 71...
Level determination section, 72... Time determination section.

Claims (1)

[Claims] 1. A first relay element that detects the differential current of the terminal currents of each winding of the transformer to be protected and outputs a breaker tripping command, and the differential current or its differential; Inputs a quantity proportional to the value, determines whether it is an internal failure or excitation inrush, and outputs a signal that allows the output of a command to trip the circuit breaker when an internal failure is determined, or a signal that allows the output of a command to trip the circuit breaker when it is determined that an internal failure occurs. and a second relay element that outputs a signal that prevents the output of a disconnector tripping command, and the second relay element samples and captures the input at appropriate time intervals, A state in which it is determined whether or not the latest consecutive sampling values exceed a predetermined detection level, and the absolute value of at least one of the plurality of sampling values exceeds the detection level. When this continues for a predetermined number of sampling times, it is determined that there is an internal failure. Alternatively, a transformer protection relay device characterized in that when the number of the plurality of sampled values whose absolute value exceeds a detection level is less than a predetermined number, it is determined that an excitation inrush has occurred. 2 The second relay element determines an internal failure when at least one of the plurality of sampling values has positive polarity and exceeds the detection level, and at least one has negative polarity and exceeds the detection level. A transformer protective relay device according to claim 1, characterized in that: