JPH0636645B2 - Protection / control device with disconnection detection function - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to an apparatus that detects a zero-phase voltage of a power system and protects and controls the power transmission system based on the detected value, and particularly to the power system. With a disconnection detection function that has the function of discriminating between the ground fault and the disconnection of the input circuit.
Regarding the control device.

(Prior Art) Conventionally, as shown in FIG. 7, the protection / control for the ground fault of the power system detects the phase voltage of each of the three phases from the tertiary circuit of the transformer PT for an instrument, and detects the phase voltage. The values are vector-synthesized to calculate the zero-phase voltage, and the digital relay or the like is operated based on the zero-phase voltage. In other words, when the combined value of each phase voltage vector exceeds a certain value, it is judged that a fault in the ground fault has occurred in the system, the relay system is activated, or an alarm is issued to protect the system.・ I was controlling.

Here, this kind of protection / control device is aimed at maintenance-free, and it is generally equipped with an "always monitoring function" for constantly detecting the presence or absence of an abnormality due to a disconnection of the input circuit. Has become.

In Fig. 7, the phase voltages of the input circuit of the protection / control device composed of digital relays are shown as _a , _b ,
_c, when the zero-phase voltage is _{0, 0,} 3 ₀ = is represented by _a + _b + _c, in a normal operating condition, since it is _a + _b + _c = 0, ₀ 0, strains ₀ does not occur unless a ground fault or the like occurs. Therefore, in the past, protection /
It was difficult to constantly monitor the input circuit of the control device for abnormalities.

Therefore, an inspection power supply is separately prepared, and the input circuit is disconnected from the power system and then switched to this power supply at regular intervals to inspect whether or not the circuit is abnormal.

However, this type of automatic inspection device generally has a complicated circuit configuration, which increases the cost of the device itself, and it is necessary to lock this circuit and disconnect it from the power system during inspection of the input circuit of the protection / control device. Therefore, it was impossible to protect and control the system from a ground fault during the inspection period.
Furthermore, since the inspection by the automatic inspection device is usually performed every 1 to 10 days for a long period of time, once an abnormality occurs in the input circuit, the abnormality can be detected until the next inspection. However, the input circuit remains defective, and it becomes impossible to detect the ground fault that occurred during this period, which is an incomplete protection of the power system.

From such a background, the zero-phase voltage generated in the system is not taken from the tertiary circuit of the transformer PT for an instrument, but the phase voltage _a ,
_A method has been proposed and adopted in which _b and _c are separately taken, these phase voltages are combined to derive 3 ₀ , and this is ⅓ to extract the zero phase voltage ₀ . According to this method, each phase voltage _a , _b , _{c of the system} is measured by the transformer P for the instrument.
Since it is taken in from the secondary circuit of T, the rated voltage (normally ) Is being applied.

Then, by a method such as comparing the values of these respective phase voltages, it becomes possible to constantly monitor the abnormality of this input circuit, and as a result, the zero-phase circuit (note that in the case of implementation by arithmetic processing of the microprocessor, It does not exist as an independent circuit), but can be monitored at all times.

In the protection / control device having such a configuration, the zero-phase voltage input circuit is simplified or unnecessary, so that the hardware is simplified and the automatic inspection device is also unnecessary. .

(Problems to be Solved by the Invention) However, in the case of adopting this method, when a disconnection failure of one wire or two wires occurs on the secondary side of the instrument transformer PT, the input circuit of the protection / control device Then zero phase voltage ₀
Is detected. As a result, there is an inconvenience that the protection / control device determines that a ground fault has occurred in the system, and the protection relay outputs a trip command.

Here, when a one-line complete ground fault occurs in the system, the zero-phase voltage V ₀ generated in the system has _a value substantially equal to the power supply voltage E _a , so the zero-phase voltage v ₀ generated in the protection / control device is Rated voltage of secondary winding On the other hand, the zero-phase voltage ₀ ′ when one or two wire disconnection failure occurs on the secondary side of the instrument transformer PT
, When the zero-phase voltage of 1-wire full ground fault and _{0, 0} '= is represented by _0/3, the instrument transformer PT zero-phase voltage of ₀ 1 line completely ground fault in the secondary circuit 33% zero-phase voltage is generated.

When the secondary circuit has a line voltage load (Δ load), this zero-phase voltage ₀ ′ is a disconnection phase (a phase) as shown in FIG.
Voltage sound phase (b, c phase) to join goes around through the _{load, v 0 '> v 0/} 3 , and becomes 33% or more of the magnitude of the zero-phase voltage v ₀ 1 line completely ground fault in .

Generally, the ground fault that occurs in the system is more than 30% (a ground fault in which 30% of the zero-phase voltage V _{0 when} one line is completely grounded occurs), so such a ground fault occurs in the system. In this case, the protection / control device detects the zero-phase voltage _{0 of the} system,
The ground fault protection or control function will be activated.

However, as described above, instrument transformer secondary circuit is more than 30% of the zero-phase voltage of the secondary circuit zero-phase voltage v ₀ 1 line complete ground fault even when disconnected v of PT ₀ 'is generated Therefore, the protection relay outputs the trip command and shuts off the system even though no ground fault has occurred in the system.

As described above, in the conventional protection / control device that detects the zero-phase voltage by synthesizing the phase voltages by the instrument transformer, there is a disadvantage that the instrument transformer malfunctions when the secondary circuit is disconnected.

The present invention has been proposed to solve the above problems, and an object of the present invention is to detect each phase voltage and each line voltage when a zero-phase voltage is generated in a secondary circuit of an instrument transformer. By comparing each with a predetermined set value,
Protection and control with a disconnection detection function that can immediately discriminate between a system ground fault and a disconnection failure of the secondary circuit, prevent malfunctions during disconnection, and realize highly reliable protection and control functions. To provide a device.

(Means for Solving the Problems) In order to achieve the above object, the present invention provides a transformer for an instrument as described in 2).
Note that the maximum phase voltage when the next circuit is disconnected is less than or equal to the maximum phase voltage when there is a 1-line ground fault in the system, and that the line-to-line voltage hardly changes in the 1-line ground fault of the high resistance grounding system. It was done by.

That is, according to the present invention, the first means for outputting the first signal only when none of the phase voltages after the zero-phase voltage is generated does not exceed the first set value, and each of the line voltages is the first voltage. The secondary circuit of the instrument transformer is provided by ANDing the second means for outputting the second signal only when the set value of 2 is exceeded and the inverted signal of the first signal and the second signal. And a third means for outputting a signal for locking the protection / control function by detecting the disconnection of the power supply, and the second set value is taken into consideration in the fluctuation of the power supply voltage and the detection error at the time of the one-wire ground fault of the system. Is set to a value smaller than the minimum value of the secondary side line voltage of the instrument transformer, and the first set value is taken into consideration in the fluctuation of the power supply voltage and the detection error when the secondary circuit of the instrument transformer is disconnected. The secondary side phase voltage is set to a value smaller than the maximum value.

Here, the first to third means are configured by AND circuits, for example.

When the zero-phase voltage is generated (Operation) system, first means, the phase voltage v _a, v _b, v _c only signal if does not exceed both the first set value (K ₁₎ " 1 ”is output. Meanwhile, the second
Means outputs the signal "1" only when each of the line voltages v _ab , v _bc , and v _ca exceeds the second set value (K ₂ ).

The third means takes a logical product of the output signal of the first means and the inverted signal of the output signal of the second means and outputs a signal.

Therefore, the third signal is output only when the output signal from the first means is "1" and the output signal from the second means is "0".
The output signal of the means becomes "1", and this case is regarded as the disconnection of the secondary circuit of the instrument transformer, and the function of the protection / control device is locked.

(Example) Hereinafter, one example of the present invention will be described with reference to the drawings.

When a ground fault occurs in the grid, zero-phase voltage is generated,
At this time, each phase voltage v _a , v _b , v on the secondary side of the instrument transformer
Any one of _c becomes a certain value (K _1g ) or more.

On the other hand, when a disconnection failure occurs in the secondary circuit of the instrument transformer, each of the phase voltages v _a , v _b , and v _c becomes a constant value (K _1l ) or less.

Therefore, originally, an arbitrary value satisfying the relationship of K _1l <K ₁ <K _1g is adopted as the set value K ₁ , and when any one of the phase voltages is K ₁ or more, a ground fault occurs in the system. It can be determined that it has occurred, and when all of the phase voltages are K ₁ or less, it can be determined that a disconnection failure has occurred in the secondary circuit of the instrument transformer.

However, the voltage of the system has a voltage fluctuation of about ± 10%,
Further, considering the detection error of ± 6% (device error of ± 5% and instrument transformer error of ± 1%), it is impossible to set the value of K ₁ as a fixed value as it is.

That is, because of these errors, all of the phase voltages are smaller than K _{1 in} spite of the ground fault, so it is determined that the secondary circuit of the instrument transformer is broken. There are cases. On the contrary, in spite of the disconnection failure, it is possible that any of the phase voltages is larger than K ₁ so that it is judged to be a system ground fault and the protection / control function is activated. .

In order to eliminate this inconvenience, means such as eliminating the above-mentioned detection error factor and voltage fluctuation factor, using a new logic in combination with the above logic for determining K ₁ and making a disconnection failure determination, etc. can be considered. Therefore, the present invention intends to eliminate the above-mentioned inconvenience by the above-mentioned means.

That is, the present invention focuses on the fact that at the time of one-line ground fault, each line voltage of the system hardly changes,
When any of the line-to-line voltages exceeds the second set value (K ₂ ), it is judged as a one-line ground fault, and in all other cases, each phase voltage has the first set value (K ₁ ). Only when it does not exceed, it is judged that the secondary circuit of the instrument transformer has a disconnection failure, and a signal for locking the protection / control function is output.

FIG. 1 shows a main configuration of an embodiment of the present invention. In FIG. 1, reference numeral 1 is a phase voltage comparison unit, and in the comparison unit 1, each phase voltage v of a secondary circuit of an instrument transformer is shown. _a , v _b ,
v magnitude of _c is compared first with the set value K _1, the phase voltage v _a, v _b, a signal "1" when v _c is smaller than the first set value K ₁ to the AND circuit 2 It is designed to output each.

Further, 3 is a line voltage comparison unit, and in this comparison unit 3,
The magnitude of each line voltage v _ab , v _bc , v _ca of the secondary circuit of the instrument transformer is compared with the _second set value K _2, and each line voltage v _ab ,
When v _bc and v _ca are larger than the second set value K ₂ , the signal "1" is output to the AND circuit 4, respectively.

The output signal of the AND circuit 2 is input to one input terminal of the AND circuit 5, and the output signal of the AND circuit 4 is inverted and then input to the other input terminal of the AND circuit 5. That, v _a, v _b, if v _c <K ₁ is satisfied, the AND circuit 2 outputs the detection signal "1" disconnected, and, AND only when the output signal of the AND circuit 4 is "0" The output signal of the circuit 5 becomes "1", and this signal is used as a signal for locking the protection / control function.

Further, if v _ab , v _bc , v _ca > K ₂ holds, then AN
Since the signal “1” is output from the D circuit 4, the lock signal is not output from the AND circuit 5 regardless of the output signal of the AND circuit 2.

Hereinafter, determination of the first and second set values K ₁ and K ₂ will be described.

<Determination of the first set value K ₁ ><Calculation of maximum phase voltage at system ground fault> There are 1-line ground fault and 2-line ground fault accidents in the system ground fault. The disconnection failure of the secondary circuit includes a 1-wire disconnection failure and a secondary disconnection failure.

(Regarding 1-line ground fault) First, calculate each phase voltage on the secondary side of the instrument transformer in case of 1-line ground fault in the system.

First, FIG. 2 (a) is a system diagram when a 1-line ground fault occurs in the system, and FIG. 2 (b) shows an equivalent circuit when a 1-line ground fault occurs in the phase a. .

In the same figure (a), G is a generator, T is a transformer, R _N is the ground resistance of the transformer T, m is the point where the transformer for the instrument is grounded, and Z _A ′ is the power source side from the m point. Of the line impedance, Z _A is the line impedance on the load side from the m point, point f is the ground fault accident point, and _Ra is the fault point resistance that occurs at the time of the ground fault.

In addition, in the figure (b), Ea is a transformer T as a power source.
, ₀ ′ _A , ₁ ′ _A , ₂ ′ _A are the zero-phase, positive-phase, and negative-phase impedances on the power supply side from the point m, _0A , _1A ,
_2A is the zero-phase, positive-phase, and negative-phase impedance on the load side from point m, _0f , _1f , and _2f are zero-phase voltage, positive-phase voltage, negative-phase voltage at point f, and ₀ , ₁ , and ₂ are at point m. Zero-phase voltage,
Positive-phase voltage, negative-phase voltage, ₀ , ₁ , and ₂ represent zero-phase voltage, positive-phase current, and negative-phase current, respectively.

Generally, in the power _{system, R N, R a »Z 0A} , Z 0 'A, Z 1A, Z 1' A, Z 2A, Z 2 'A is established.

In addition, at the time of a one-line ground fault, the following relationship holds between ₀ , ₁ , and ₂ . ₀ = ₁ = _{2 0, 1, 2} is represented by _{0 = 3R N + 0 'A} + 0A ≒ 3R N 1 = 1' A + 1A 2 = 2 'A + 2A, 0 is ₀ = _a / _{(0 + 1 + 2 + 3R} a) ≒ a / (3R N + 3R a) = a / {3R N (1 + k a)} ( _{where, k a = R a / R} N) becomes.

In order to obtain each phase voltage at the relay installation point when there is a one-wire ground fault, first find ₀ , ₁ , and ₂ at the relay installation point.

As is clear from FIG. 2 (b), _{0, 0} = _0f + but _0A is _{0 ≒ 0f + 0A a / 3R} N, 0f = - (3R N + 0 'A + 0A) 0 = - a Since / (1 + k _a ), ₀ = _−a / (1 + k _a ). _{1, 1} = _1f + _1A · ₁ is a _{≒ 1f, 1f = a - (} 1A + 1A) 1 because it is ≒ _a, a ₁ = _a.

Further, ₂ is ₂ = _2f + _{2A 2 ≈2f} , but _2f = − ( _2A + _2A ) ₂ ≈0, so ₂ = 0.

Therefore, each phase potential _a , _b , _{c at the} relay installation point
Is Becomes

Since the complete ground fault is _{k a = 0, a = 0} b = a - - (1 + a) · a (1 + a 2) · a c =.

Further, the 30% ground fault, and _{a = -0.3 a + a = 0.7} a b = -0.3 a + a 2 a c = -0.3 a + a a.

Note that Fig. 2 (C) is a vector diagram when a 30% ground fault occurs.
At the time of a line ground fault, the ground fault phase voltage always drops and the voltages of the other two phases rise.

As is clear from the figure, when the a-phase 1-line 30% ground fault occurs, the secondary side phase voltage of the instrument transformer is v _a = 44.45 [V], v _b =
v _c = 74.87 [V].

(Regarding 2-wire ground fault) Next, the secondary-side phase voltages of the transformer for an instrument at the time of 2-wire ground fault are calculated.

First, Fig. 3 (a) shows the system diagram when a two-wire ground fault occurs in the system, and Fig. 3 (b) shows the equivalent circuit when a two-wire ground fault occurs in the b-phase and the c-phase. There is.

At the time of a two-wire ground fault, the following relationship is established between the zero-phase voltage _0f , the positive-phase voltage _1f , and the negative-phase voltage _{2f at} the ground fault point. _0f = _1f = _{2f Further} , regarding the zero-phase impedance ₀ , the positive-phase impedance ₁ and the negative-phase impedance ₂ of the system, as in the case of the one-line ground fault, R _N , R _a >> Z _0A , Z ₀ ′ _A , Z _{1A, Z 1 'A, Z} 2A, Z 2' A is established.

In the case of 2-wire complete ground fault, positive phase current ₁ is Here, ₁ When _{≒ 2, 1 = a / 2} 1 0 ≒ 0 2 ≒ - 1 = - a _a / ₍₁ + _2).

In order to obtain each phase voltage at the relay installation point when a two-wire ground fault occurs, first find ₀ , ₁ , and ₂ at the relay installation point. ₀ is ₀ = _0f + _0A · ₀ ≈ _0f , but _0f = − ( ₂ ′ _A + _2A ) · ₂ = _a / 2, so ₀ = _a / 2.

Also, _{1, 1 = 1f + 1A · 1} ≒ 1f + 1A a / 2 1 However, because it is _1f = _a / 2, Becomes

Further, ₂ becomes ₂ = _2f + _{2A 2 ≈2f} + _{2A a} / 2 ₁ .

However, since _2f = _a / 2, _1A = _2A , Becomes

Therefore, each phase voltage _a , _b , _{c at the} relay set point
Is Becomes

Note that FIG. 3C is a vector diagram at the time of a two-line complete ground fault.

The characteristics at the time of two-wire incomplete ground fault are as follows: failure point resistance (arc resistance,
The phase voltage varies depending on how it goes into the tower pedestal resistance, etc., but the failure phase (b, c phase) voltage drops in both cases, regardless of whether it is a complete ground fault or an incomplete ground fault. The voltage rises.

When R _f = 0, R _1f = R _2f , and a ground fault occurs that causes a zero-phase voltage equivalent to 30% of the one-line complete ground fault, a healthy phase voltage
_a is Becomes

In this case, the secondary side phase voltage of the instrument transformer is v _a = 82.6
[V], v _b = v _c = 12.7 [V].

Phase ₀ of the zero-phase voltage ₀ at this time, the phase voltage V _a phase
Although become almost the same phase as _a, phase is in a different spot out-of-phase ground fault
_There is _a phase difference between ₀ and _a . In this case, the secondary side phase voltage of the instrument transformer will be v _a <82.6 [V], but in the actual system, it will almost never drop to the voltage rise value (74.87 [V]) at the time of one-line ground fault. Absent.

<Calculation of the maximum phase voltage in the disconnection> Next, each phase voltage _a of the secondary circuit of the instrument transformer when disconnection failure ', _b', and calculates the _c '.

Here, Fig. 4 shows the protection of digital relays, etc.
In the figure, PT is an instrument transformer, _a , _b and _c are digital relay loads, and _ab , _bc and _ca are line voltage loads ( Δ load), F ₁ and F ₂ are failure points (disconnection points).

(About 1 wire disconnection) Figure 5 (a) is an equivalent circuit when one wire (a phase) is disconnected. In the figure, _0B , _1B and _2B are zero phase, normal phase and reverse phase when looking at the power supply side from the fault point. Phase impedances, _0L , _1L , and _2L are the zero-phase, positive-phase, and negative-phase impedances when the relay side is viewed from the fault point.

At the time of one wire disconnection, when the Δ load is not connected to the secondary side of the instrument transformer, that is, when the phase voltage load (Y load), the disconnection phase voltage _a is shown in the vector diagram of Fig. 5 (b). As shown, v _a ≈0. Even when there is a Δ load, F in FIG.
If an accident occurs at _two points, the zero-phase voltage is not affected by the Δ load, so it can be handled in the same way as when the Δ load is not connected.

On the other hand, if there is a Δ load or if an accident occurs at point F _{1 in} Fig. 4, the healthy phase voltage will also flow into the disconnection phase through the Δ load, so the disconnection phase voltage ₁ should have a certain value. become.

Fig. 5 (c) shows an example of a vector diagram of each phase voltage when a Δ load exists, and _a changes depending on the ratio between Δ loads and the ratio between Δ load and Y load. But the sound phase voltage Never exceeds.

Thus, v _a at the time of a phase disconnection is Becomes

However, if there is an LC resonance phenomenon between the Δ load and the Y load, the sound phase voltage may be exceeded, but in the actual system there is no such impedance distribution.

(About 2-wire disconnection) In the case of 2-wire (a, b-phase) disconnection, the sound phase is only for one phase, and the basic tendency of each phase voltage is the same as when 1-wire disconnection. FIG. 6 (a) is an equivalent circuit when the two wires are disconnected.
(B) is an example of a vector diagram when there is no Δ load.
(C) shows an example of a vector diagram when there is a Δ load.

Also in this case Always holds.

The maximum value of the secondary side phase voltage of the transformer for the case of the 1-wire ground fault and the 2-wire ground fault accident of the system, which was obtained as described above, and the 1-line disconnection and the 2-side disconnection fault for the meter Based on the maximum value of the secondary side phase voltage of the transformer, it is possible to discriminate between the system ground fault and the secondary circuit disconnection failure of the instrument transformer by the following phase voltage comparison method.

That is, when the protection / control circuit detects an abnormality in the phase voltage, all the phase voltages have a constant value K ₁ If it is smaller, it is regarded as a wire break, and if it is larger, it is regarded as a system ground fault.

Here, the value of K ₁ is the maximum phase voltage v _m at the time of a ground fault in the system.
It is necessary to make it smaller than (K _1g mentioned above) and larger than the maximum phase voltage v _m ′ (K _1l mentioned above) at the time of disconnection. Therefore, 63.5 <K ₁ <74.9.

However, the voltage of the system has a voltage fluctuation of about ± 10%,
Considering the detection error of 6% (device error ± 5%, instrument transformer error 1%), the total error is (0.9 × 0.94-1) × 100 = -15.4%, from (1.1 × The range is 1.06-1) × 100 = 16.6%, and it is difficult to set the value of K ₁ as a fixed value.

For example, here K ₁ is the central value between 63.5 and 74.9,
That is, if K ₁ = (63.5 + 74.9) /2=69.2 [V] is set, the maximum phase voltage at disconnection may be detected as 63.5 × 1.1 × 1.06 = 74.04 [V] at the maximum. In addition, the maximum phase voltage at the time of the ground fault may be detected as 74.9 × 0.9 × 0.94 = 63.3 [V] at the lowest.

If «a second decision setting K _2» 1 line ground occurs in the system, the equivalent circuit shown in FIG. 2 _{(b), a = 0 b = (} - 1 + a 2) · a c = ( -1 + _a) · a Therefore, _{ab = ab = (1-a} 2) · a bc = bc = (a 2 -a) · a ca = ca = (a-1) · a Therefore, | _ab | ＝ | _bc | ＝ | _ca |

Even at the time of 30% ground fault, the relationship between each phase voltage and each line voltage hardly changes as shown in the vector diagram of Fig. 2 (c).

In this way, when a one-line ground fault occurs in the high resistance grounding system, the magnitude of each line voltage does not change.

Therefore, power supply voltage fluctuation (± 10%) and detection error (± 6%)
In consideration of the above, the minimum value of the line voltage V is 110 × 0.90 × 0.94 = 93.06 [V], and therefore K ₂ = 93.0 [V] can be set.

In this way, by adopting the above-mentioned means, the one-line ground fault can be surely detected, so that the value of K ₁ can be made smaller than the maximum phase voltage at the time of disconnection.
The maximum phase voltage is 63.5 × 1.10 × 1.06 = 74.04 [V], and for example, K ₁ = 74.0 [V] can be set.

In this way, when K ₁ and K ₂ are set, it may be considered as a disconnection when a two-wire ground fault occurs.

That is, in a two-wire ground fault where a zero-phase voltage equivalent to 30% of the zero-phase voltage when a one-wire complete ground fault occurs, the maximum phase voltage is
It becomes 82.6 [V]. If the power supply fluctuation of -10% and the detection error of -6% are taken into consideration, the maximum phase voltage is 69.9 [V]. For this reason, it is judged that all three phases are below 74.0 [V] and that there is a disconnection,
A lock command will be issued to the protection / control device, but in the case of a two-wire ground fault, a short-circuit accident will occur at the same time, so protection / control processing for a short-circuit will be given priority, which is practically acceptable. .

(Effects of the Invention) As described above, according to the present invention, when a zero-phase voltage is generated in the secondary circuit of the instrument transformer, it is a ground fault of the system or a secondary circuit disconnection failure of the instrument transformer. Since it is possible to discriminate between them, it is possible to reliably prevent a malfunction at the time of disconnection and provide a highly reliable protection / control device.

In addition, the method of deriving the zero-phase voltage by synthesizing the input phase voltages can be applied, and the zero-phase input circuit can be eliminated, and the automatic inspection device is not required. The device can be supplied.

[Brief description of drawings]

FIG. 1 is a diagram showing a main part of the configuration of one embodiment of the present invention, FIG. 2 (a) is a system diagram in the case of a system 1 line ground fault, FIG. 2 (b) is the same equivalent circuit, and FIG. ) Is also a vector diagram, Fig. 3 (a) is a system diagram when a system 2 wire ground fault occurs, and Fig. 3 (b) is an equivalent circuit.
The same figure (c) is also a vector diagram, FIG. 4 is an explanatory diagram of the input circuit of the protection / control device, and FIG. 5 (a) is an equivalent circuit of the secondary circuit of the transformer for instrument when the wire is broken, (B) and (c) are also vector diagrams, Fig. 6 (a) is an equivalent circuit when the secondary wire of the transformer for the instrument is broken, and (b) and (c) are vector diagrams.
7 and 8 are explanatory diagrams of an input circuit of a protection / control device for explaining a conventional example. 1 ... Phase voltage comparison unit, 2, 4, 5 ... AND circuit, 3 ...
... Line voltage comparison section

Claims (1)

[Claims] 1. A device for protecting and controlling a system by detecting a zero-phase voltage from each phase voltage in a three-phase power system, and only when all of the values of each phase voltage do not exceed a first set value. First means for outputting a first signal; second means for outputting a second signal only when all of the line voltages exceed a second set value; the first signal and the second signal And a third means for detecting the disconnection of the secondary circuit of the transformer for an instrument which constitutes the input circuit by taking a logical product of the signal of the above and the inversion signal and outputting a signal for locking the protection / control function. The second set value is set to a value smaller than the minimum value of the secondary side line voltage of the transformer for an instrument in consideration of the power supply voltage fluctuation and the detection error at the time of one-line ground fault of the system, The set value of 1 is the power supply voltage fluctuation and detection error when the secondary circuit of the transformer for instrument is disconnected. A protection / control device with a disconnection detection function, which is set to a value smaller than the maximum value of the secondary side phase voltage in consideration of the above.