JPH0438118A - Variation width detector - Google Patents

Abstract

PURPOSE:To output a fault signal accurately by multiplying a line voltage, obtained from each phase current and ground voltage of a distribution line, by a zero-phase current, extracting DC component through a filter, and comparing a difference between a delayed value and not delayed value with a predetermined value. CONSTITUTION:A ground directional relay 12 receives ground voltages VR-VT obtained from voltage division capacitors CT-CRG for each phase of three-phase distribution line 10 and current signals IR-IT obtained from CTR-CTT. Arithmetic section 14 of the relay 12 performs vector operation phase shift 22-26 and vector operations 28, 30, and operates reference voltages VRS-VTR and zero-phase voltage VO and current Io from the ground voltages VR-VT. An arithmetic section 16 multiplies 32 the reference voltage and the zero-phase current and feeds the sum to an LPF 34 output therefrom is then fed to a level memory section 36 and an arithmetic unit 38. The arithmetic unit 38 produces a difference between the output from the LPF 34 and a signal delayed through the memory section 36, and then the difference is compared 40 with a set level Ve and a fault signal is produced if the difference is large. Consequently, ground fault can be detected accurately regardless of the residual electric amount in the distribution line.

Description

[Detailed Description of the Invention] [Field of Industrial Application] The present invention relates to a variation width detection device, and in particular, it is capable of detecting ground faults with high sensitivity even in systems where residual zero-sequence voltage or residual zero-sequence current exists in distribution lines. The present invention relates to a change width detection device suitable for detecting a change width.

[Conventional technology]

In general, high-voltage power distribution systems are wired in a dendritic pattern, and high-voltage power distribution systems consisting of three-phase distribution lines have parts that are geometrically asymmetrical with respect to the ground. Capacitance may become unbalanced. For this reason,
In such a system, residual zero-sequence voltage and residual zero-sequence current always exist.

By the way, in order to detect a ground fault accident in such a system, a ground fault direction relay is generally used, and it is desired that the detection sensitivity of this relay be high from the viewpoint of safety.

[Problem to be solved by the invention]

However, in the prior art, ground faults are detected using ground fault directional relays even in systems where residual voltage or current always exists. Therefore, when a ground fault occurs in a power system, phase discrimination is performed using the vector composite amount of the residual electricity and the zero-sequence electricity generated due to the ground fault as input. In the event of a high resistance ground fault in the vicinity, phase discrimination may be incorrect. In order to prevent such errors in phase discrimination, methods have been adopted to reduce the detection sensitivity so that the phase discrimination performance is not affected by residual voltage or current. Because the zero-sequence voltage or current of , or may not occur, and there is a risk that a ground fault cannot be reliably detected.

The purpose of the present invention is to provide a change in which, even if residual zero-sequence voltage and residual zero-sequence current are always present in the power distribution system, ground faults can be reliably detected without being influenced by the magnitude of these residual amounts of electricity. An object of the present invention is to provide a width detection device.

[Means to solve the problem]

In order to achieve the above object, the present invention provides a first device that includes a ground voltage detection means for detecting the ground voltage of each phase of a distribution line, and detects the line voltage of each phase from the detection output of the ground voltage detection means. A line voltage calculation means to calculate, a phase current detection means to detect the phase current of each phase of the distribution line, a zero phase detection means to detect the zero sequence current from the detection output of the phase current detection means, and a line voltage calculation means. a multiplication means for multiplying the output of the means and the output of the zero-sequence current detection means; a filter means for extracting a DC component from the output of the multiplication means; a delay means for delaying the output of the filter means for a certain period of time; and an output of the delay means. and an accident signal generation means that generates an accident signal when the output of the deviation calculation means exceeds a set level. It is.

The second device includes a ground voltage detection means for detecting the ground voltage of each phase of the distribution line, a line voltage calculation means for calculating the line voltage of each phase from the detection output of the ground voltage detection means, and a line voltage calculation means for calculating the line voltage of each phase from the detection output of the ground voltage detection means. A phase current detection means that detects the phase current of each phase, a zero-phase detection means that detects the zero-sequence current from the detection output of the phase current detection means, an output of the line voltage calculation means, and an output of the zero-sequence current detection means. a filter means for extracting a DC component from the output of the multiplication means, a delay means for delaying the output of the filter means for a certain period of time, and a hold command to hold and output the output of the delay means when the hold command is input. and a hold means that outputs the output of the delay means as it is in response to a hold release command, a deviation calculation means that outputs the deviation between the output of the delay means and the output of the hold means, and when the output of the deviation calculation means exceeds a set level. an accident signal generation means that generates an accident signal when the accident signal is received, outputs a hold command while the accident signal is being generated, continues to generate the hold command for a certain period of time when the generation of the accident signal is stopped, and then releases the hold. The variation range detection device includes a hold command means for outputting a command.

The third device includes a ground voltage detection means for detecting the ground voltage of each phase of the distribution line, a line voltage calculation means for calculating the line voltage of each phase from the detection output of the ground voltage detection means, and a ground voltage detection means. zero-sequence voltage detection means for detecting the zero-sequence voltage of the distribution line from the output of the means; multiplication means for multiplying the output of the line voltage detection means by the output of the zero-sequence voltage detection means; a delay means for delaying the output of the filter means for a certain period of time; a deviation calculation means for calculating the deviation between the output of the delay means and the output of the filter means; The variation range detection device includes an accident signal generating means for generating an accident signal when the accident occurs.

The fourth device includes a ground voltage detection means for detecting the ground voltage of each phase of the distribution line, a line voltage calculation means for calculating the line voltage of each phase from the detection output of the ground voltage detection means, and a ground voltage detection means. zero-sequence voltage detection means for detecting the zero-sequence voltage of the distribution line from the output of the means; multiplication means for multiplying the output of the line voltage detection means by the output of the zero-sequence voltage detection means; , a delay means that delays the output of the filter means for a certain period of time, and a hold that holds and outputs the output of the delay means when the hold command is input by a hold command, and outputs the output of the delay means as it is by a hold release command. means, deviation calculation means for outputting a deviation between the output of the delay means and the output of the hold means, accident signal generation means for generating an accident signal when the output of the deviation calculation means exceeds a set level, and an accident signal. and a hold command means for outputting a hold command during the generation of an accident signal in response to the occurrence of the accident signal, and for continuing to generate the hold command for a certain period of time when the generation of the accident signal is stopped, and then outputting a hold release command. It is composed of

A fifth device including the second or fourth device includes gate means for outputting a signal according to the logical sum of the input signals to the hold means between the hold command means of each phase and the hold command means, A change range detection device is constructed in which the output of the hold command means of each phase is connected to the input of its own gate means and the gate means of other phases.

A sixth device including the first, second, third, or fourth device is a change range detection device using a bandpass filter as a delay means.

An eighth device including the second, fourth, fifth, or sixth device monitors the occurrence of an accident signal and issues a hold release command to the hold command means when the occurrence of the accident signal continues for a set time or longer. This is a variation range detection device having a hold release command means for forcibly outputting the hold release command.

An eighth device including any one of the first to seventh devices includes a level comparator that generates an accident signal when the output of the deviation calculation device exceeds a positive set level. and a level comparator that generates an accident signal when the output of the deviation calculation means exceeds a set negative level.

[Effect]

The line voltage of each phase was determined from the ground voltage of each phase of the distribution line, the zero-sequence current and the line voltage were multiplied using this line voltage as a reference signal, and the DC component was extracted from this multiplied value. The signal is delayed for a certain period of time, the deviation between the delayed signal and the undelayed signal is determined, and an accident signal is generated when this deviation exceeds a set level. In other words, even if there is a residual zero-sequence voltage and a residual zero-sequence current in the power distribution system, the amount of residual electricity is used as the standard value during steady state, and the change from the standard value is detected, and if this change exceeds the set level, Occasionally, an accident signal is generated as a ground fault. Therefore, even if a residual zero-sequence voltage and a residual zero-sequence current exist in the power distribution system, a ground fault in the power distribution system can be reliably detected regardless of the level of the residual electricity amount. Such detection can be performed in the same way even when the reference signal and the zero-sequence voltage are multiplied and a ground fault is detected from this multiplied value.

If it has a hold means and a hold command means,
The output of the delay means is held by a hold command, the deviation between the held signal and the output of the delay means is determined, and an accident signal is generated when this deviation exceeds a set level. In other words, if residual zero-sequence voltage and residual zero-sequence current exist in the power distribution system, these levels are stored as steady-state levels, and when a ground fault occurs, the change from the stored levels is detected. When this change exceeds a set level, a fault signal is generated to indicate a ground fault. Furthermore, when the ground fault has recovered, the level at the time of the ground fault will continue to be stored for a certain period of time even after the ground fault has stopped, and then the stored level will be erased and a new one will be input. Ground faults are detected using the signal as a reference level. Therefore, subsequent ground faults can be detected at the steady state level without setting the reference level after accident recovery to a high level. or,
In this case, if a gate means is provided, all phases can simultaneously hold and release the hold of the input signal of the phase in which the fault has been detected, thereby preventing phases other than the fault phase from malfunctioning. .

〔Example〕

Hereinafter, one embodiment of the present invention will be described based on the drawings.

In FIG. 1, the R phase, S phase, and T phase of the three-phase distribution line 10 are connected to voltage dividing capacitors CT that constitute ground voltage detection means,
C8, CR, CTG, C5G, CRG are connected, and the line voltages VR, VS, which are divided by each capacitor,
VT is input to the ground fault direction relay 12 as a ground voltage. Further, the three-phase distribution line 10 is provided with current transformers CTR, CTS, and CTT that constitute phase current detection means, and the output of each current transformer is sent to the relay 12 as phase currents IR, IS, and IT.
has been entered. The earth fault direction relay 12 includes a calculation section 14 shown in FIG. 2, and detection sections 16 and 18 shown in FIG.
．． 20.

The calculation unit 14 includes vector calculation phase shifters 22, 24.26 and vector calculation units 28.30.
Line voltage VR8, VST, as a reference signal for each phase from T.
It constitutes a line voltage calculation means for calculating the VTR. That is, in this embodiment, when a ground fault occurs, the phase voltage changes, but the line voltage does not change, so the line voltage is determined as the reference signal for each phase. And when finding this line voltage,
The line voltage between each phase is determined by vector calculation from the detected values of the line voltages VR, VS, and VT of each phase, and the line voltage is determined by shifting the phase of the line voltage between each phase by 3°. Line voltages VR5, VST, and VTR that are in phase with the voltage are output.

On the other hand, the vector calculator 28 calculates the line voltages VR and VS.

It is configured as a zero-sequence voltage detection means for detecting the zero-sequence voltage vO from the vector value of VT, and the vector calculator 30 detects the zero-sequence current IO from the vector values of the phase currents IR, IS, and IT.
It is configured as a zero-phase current detection means for detecting. The output of the calculation unit 14 is output from the detection units 16 and 1 of each phase.
Supplied on 8.20. The R-phase detection section 16 includes a multiplier 32, a low-pass filter 34, a level storage 36, an arithmetic unit 38, and a level comparator 40, and also includes an S-phase detection section 18 and a T-phase detection section 20. R phase detection section 1
It is made up of the same components as 6.

The multiplier 32 is configured as a multiplier that multiplies the R-phase and S-phase line voltage VR3 and the zero-sequence current ■0 as the R-phase reference signal, and outputs the multiplied signal to the low-pass filter 34. The low-pass filter 34 is configured as a filter means for extracting a DC component from an input signal. That is, since the multiplied value of the multiplier 32 includes twice as many harmonics, the low-pass filter 34 removes the harmonics and extracts only the DC component. The pressure of the low-pass filter 34 is input to a level storage device 36 and a calculator 38.

The level memory 36 includes a delay circuit 42. having a resistor R and a capacitor C. Sample hold 44, OR gate 46,
It is configured to include a limited time return timer 48. The pressure of the sample hold 44 is input to the negative input terminal of the calculator 38, and the output of the level comparator 40 is input to the sample hold 44 as well as the timer 48 and the OR gate 46.
is entered via. A signal from the low-pass filter 34 is input to the sample hold 44 after being delayed for a certain period of time by a delay circuit 42. When the input level of the sample hold terminal S/H is "0", that is, the hold release command is input. When the input signal is input, the input signal is output as is to the calculator 38, and when the input level of the sample hold terminal S/H is "1" 1, that is, when the hold command is input, the input signal at the time of input of the hold command is output. It is configured as a holding means for holding the level of and outputting the held signal to the arithmetic unit 38.

The arithmetic unit 38 is configured as a deviation calculation means that outputs a signal corresponding to the deviation between the 8-power signal of the low-pass filter 34 and the output signal of the sample hold 44, and the level comparator 40 is configured to output a signal corresponding to the deviation between the output signal of the low-pass filter 34 and the output signal of the sample hold 44. Compare with Ve,
When the comparison signal of the arithmetic unit 38 exceeds the set level Ve, the signal of "P1" is sent to the terminal IA and the timer 4 as an accident signal.
It is configured as an accident signal generating means to be output to 8.

When the fault signal is input, that is, when the output of the level comparator 40 is 1'', the time-limited return timer 48 instantly issues a hold command and sends the 1'' signal to the OR gate 46 and S.
It is configured as a hold command means that outputs a signal to the OR gates of phase and T phase, continues to generate a hold command for a certain period of time when the generation of the fault signal is stopped, and then outputs a "0" signal as a hold release command. There is.

In the above configuration, when there is a residual zero-sequence voltage and a residual zero-sequence current in the distribution line 10, the output of the low-pass filter 34 is as shown in FIG. A signal with the waveform shown in is output. For example, the R phase has a level offset in the positive direction, the T phase has a level offset in the negative direction, and the S phase has a signal of approximately zero. Such an offset occurs because, as shown in FIG. 6, a residual zero-sequence current Ioe exists in the distribution line 10, and even in a steady state, V
This is because the calculated values of RX Ioe, VSXIoe, and VTXIoe are generated at the output of the low-pass filter 34.

In such a state, when a ground fault occurs in the R phase of the distribution line 10, the fault current Ios is added to the residual zero-sequence current Ioe, as shown in FIG. A signal is generated in which the R phase level is high and the S phase and T phase levels are low. At this time, as shown in FIG. 7, the output level of the low-pass filter 34 suddenly increases, and this signal is input to the arithmetic unit 38 as it is.

On the other hand, a signal delayed for a certain period of time by the delay circuit 42 is input to the sample hold 44, as shown by a broken line. The deviation at this time is calculated by the calculator 38, and if the calculated value exceeds the set level Ve, the level comparator 4
A fault signal from 0 to 11171 is generated. As a result, the signal t(117) from the timer 48 is input to the sample hold terminal S/H via the OR gate 46, and the level SHo at the time of occurrence of the ground fault is held as the reference level.

Therefore, while a ground fault is occurring, the level comparator 4
From 0 to 1, a signal of "1" is continuously output. At this time, the signal at the terminal IA is input to a controller for controlling a circuit breaker or the like, and control is executed to shut off the circuit breaker or the like when an accident signal occurs. Furthermore, at this time, the output of the timer 48 is input to the S-phase and T-phase OR gates, and the S-phase and T-phase sample and hold also hold the level at the time T1 when the ground fault occurs as a reference level.

When the ground fault is recovered, the output level of the delay circuit 42 gradually decreases from time T2, but the output of the timer 48 remains "1" until the output level of the delay circuit 42 returns to the reference level SHo before the ground fault occurred. will be kept as is. Then, at time T3, when a certain period of time T has elapsed from time T2, the output of the timer 48 is inverted to 110'', and the sample hold 4
4 is commanded to release the hold, and thereafter the output of the delay circuit 42 is inputted as is to the arithmetic unit 38.

In this way, according to the present embodiment, even if there is a residual amount of electricity in the distribution line IO, this residual component is set as the reference level, a change from this reference level is detected, and this change is detected. Since it is assumed that a ground fault has occurred when the value exceeds the set level Ve, a ground fault can be reliably detected without being influenced by the level of the amount of residual electricity in the wiring line 10. Furthermore, since a ground fault is detected from the multiplication value of the zero-sequence current Io and the line voltage, it is also possible to determine the direction in which the ground fault has occurred.

For example, by installing a plurality of relays 12 on the distribution line 10, it is possible to determine the direction in which a ground fault occurs based on which relay 12 detects the ground fault when the fault occurs.

Furthermore, according to this embodiment, even after a ground fault occurs, the timer 4 remains active.
Since the output of 8 is held at "1", a high level is not held as the reference level of the sample hold 44 after the ground fault is recovered, and the ground fault continues after the ground fault is recovered. Even if a ground fault occurs, it can be reliably detected.

Furthermore, it is possible to prevent erroneous detection that a ground fault has occurred again during recovery from a ground fault.

That is, if there is no timer 48, as shown in FIG. 8, when a ground fault occurs in the R phase and the ground fault recovers, the level of the T phase changes in the positive direction, so this level When the set level Ve is exceeded, T
If a ground fault occurs in a phase, a fault signal will be generated from the T-phase level comparator. For this reason, timer 48
By providing this, even if the output of the low-pass filter 34 changes in the positive direction when the ground fault is recovered, it is possible to prevent the ground fault from being erroneously detected.

Further, in the above embodiment, the output of the timer 48 of each phase is
Since it is input to the R gate 46, when a ground fault is detected in any phase, the sample hold 3 of each phase is
4 performs hold and hold release operations at the same time. Therefore, when a ground fault is detected in any phase, it is possible to prevent other phases from malfunctioning.

Next, another embodiment of the present invention will be described based on FIGS. 9 and 10.

In this embodiment, a bandpass filter 50. A level comparator 38.degree. 52 and a flip-flop 54 are provided, and the output of the flip-flop 54 is outputted to a timer 48 and a terminal IA, and the other configurations are the same as those of the previous embodiment.

The bandpass filter 50 is a non-vibration type bandpass filter without vibration damping, and has a Q of 0.7 or less.

Since the bandpass filter 50 cuts the DC component,
When a signal as shown in FIG. 10 (, A) is input from the low-pass filter 34, the signal is generated only when the signal level changes, and when the signal level is constant, the DC component is cut. It is designed to output a signal as shown in (13). When the output level of the bandpass filter 50 exceeds the positive set level +Ve, the level comparator 38 outputs an error signal Ld.
The IIT signal is output, and the flip-flop 54 is set. As a result, the flip-flop 54 outputs the signal LL I IT as the fault signal.

On the other hand, when the ground fault is recovered, the output level of the bandpass filter 50 changes to the negative side, and when the level becomes equal to or less than the negative setting level -Ve of the level comparator 52, the flip-flop 54 is reset, and the flip-flop 54 is reset. 54 outputs a signal of +10 IT. Note that the timer 48 indicates that the level of the flip-flop 54 changes to 0'' when a certain period of time has elapsed after the level reached 0''.

In this embodiment as well, a ground fault can be reliably detected without being influenced by the level of residual electricity in the distribution line 10, as in the previous embodiment.

In addition, in each of the above embodiments, the zero-phase current equipment 0 and the line electrical equipment
In the above description, a ground fault fault is detected based on the multiplication value of the zero-sequence voltage Vo and the line voltage, but it is also possible to detect a ground fault fault based on the multiplication value of the zero-sequence voltage Vo and the line voltage. Furthermore, the zero-sequence current ■0
We have described a device that detects zero-sequence current to detect zero-sequence current, but instead of detecting zero-sequence current from line current, it is also possible to use a zero-sequence current detector ZCT to directly detect zero-sequence current from ZCT. It is possible.

Further, in each of the above embodiments, when the output of the level comparator 40 or the flip-flop 54 is monitored and the occurrence of the accident signal continues for a certain period of time or more, a hold release command is issued to forcibly set the output of the timer 48 to 'O'. If a means is provided, even if the level of residual electricity increases from the level before the ground fault occurs due to the state of the distribution line 10 after the ground fault has been recovered, the increased level can be used as the reference level for the sample. The hold 44 can be returned to its original state.

For example, a level comparator 4 is connected to the output side of the arithmetic unit 38 in FIG.
0.52 is connected to the output terminal of each level comparator 40. 52, the direction in which the ground fault occurred can be determined even if the value of the zero-sequence current 1o becomes positive or negative depending on the location where the ground fault occurs. That is, when the output of the low-pass filter 34 changes slightly to the positive side due to the occurrence of a ground fault,
A ground fault can be detected by the level comparator 40, and when it changes to the negative side, the ground fault can be reliably detected by the output of the level comparator 52. It becomes possible to determine the

〔Effect of the invention〕

As explained above, according to the present invention, the amount of residual electricity in the power distribution system is set as a reference level, a change from this reference level is detected, and when this detection level exceeds a set level, a ground fault is detected. Therefore, even if there is residual electricity in the distribution line, a ground fault can be reliably detected regardless of the level of the residual electricity.

Furthermore, even when a ground fault fault is recovered, the hold command continues to be issued for a certain period of time, and then the hold is released, which prevents phases other than the faulty phase from malfunctioning when the ground fault fault is recovered. can.

If the accident signal continues to occur for a certain period of time, the hold state will be forcibly released.
Even if the level of residual electricity changes when recovering from a ground fault,
It is possible to return to the original state using the changed level as the reference level.

The accident signal generating means includes a level comparator for determining whether the output of the deviation calculating means exceeds a positive set level, and a level comparator for determining whether the output of the deviation calculating means exceeds a negative set level. If a detector is installed, the direction in which a ground fault occurs can be easily determined.

[Brief explanation of the drawing]

FIG. 1 is an overall configuration diagram showing an embodiment of the present invention. Figure 2 is a block diagram of the arithmetic unit, Figure 3 is a block diagram of the detection unit, Figure 4 is a diagram explaining the configuration of the level storage unit, Figure 5 is a waveform diagram showing the output waveform of the low-pass filter, and Figure 6 is a diagram showing the output waveform of the low-pass filter. A vector diagram showing the amount of residual electricity in the power distribution system, Figure 7 is a waveform diagram of each part in Figure 4, Figure 8 is a waveform diagram of each part when there is no timer 48,
FIG. 9 is a main part configuration diagram showing another embodiment of the present invention, and FIG.
The figure is a waveform diagram for explaining the operation of FIG. 9. 10... Distribution line, 12... Ground fault direction relay, 14...
...Arithmetic section, 16, 18.20...Detection section, 34...
Low-pass filter, 36... Level storage device, 38...
- Arithmetic unit, 40... Level comparator, 42... Delay circuit, 44... Sample hold, 46... OR gate, 48... Time-limited return timer, 50... Band pass filter, 52 ...Level comparator, 54...Flip-flop.

Claims (1)

[Scope of Claims] 1. Ground voltage detection means for detecting the ground voltage of each phase of a distribution line; line voltage calculation means for calculating the line voltage of each phase from the detection output of the ground voltage detection means; A phase current detection means for detecting the phase current of each phase of the electric wire, a zero-sequence current detection means for detecting the zero-sequence current from the detection output of the phase current detection means, and an output of the line voltage calculation means and the zero-sequence current detection means. a filter means for extracting a DC component from the output of the multiplication means, a delay means for delaying the output of the filter means for a certain period of time, and a deviation between the output of the delay means and the output of the filter means. A variation range detection device having a deviation calculating means for calculating the deviation, and an accident signal generating means for generating an accident signal when the output of the deviation calculating means exceeds a set level. 2. Ground voltage detection means for detecting the ground voltage of each phase of the distribution line; line voltage calculation means for calculating the line voltage of each phase from the detection output of the ground voltage detection means; Phase current detection means for detecting current; zero-sequence current detection means for detecting zero-sequence current from the detection output of the phase current detection means; and multiplication of the output of the line voltage calculation means and the output of the zero-sequence current detection means. a multiplication means; a filter means for extracting a DC component from the output of the multiplication means; a delay means for delaying the output of the filter means for a certain period of time; A hold means outputs the output of the delay means as it is in response to a release command, a deviation calculation means outputs the deviation between the output of the delay means and the output of the hold means, and an accident signal is generated when the output of the deviation calculation means exceeds a set level. An accident signal generation means that generates an accident signal, receives an accident signal, outputs a hold command while the accident signal is occurring, and when the generation of the accident signal is stopped, continues to generate the hold command for a certain period of time, and then outputs a hold release command. A change width detection device having a hold command means for 3. Ground voltage detection means for detecting the ground voltage of each phase of the distribution line, line voltage calculation means for calculating the line voltage of each phase from the detection output of the ground voltage detection means, and from the output of the ground voltage detection means. Zero-sequence voltage detection means for detecting the zero-sequence voltage of the distribution line, multiplication means for multiplying the output of the line voltage detection means and the output of the zero-sequence voltage detection means, and a filter for extracting a DC component from the output of the multiplication means. a delay means for delaying the output of the filter means for a certain period of time; a deviation calculation means for calculating the deviation between the output of the delay means and the output of the filter means; and when the output of the deviation calculation means exceeds a set level. and an accident signal generating means for generating an accident signal. 4. Ground voltage detection means for detecting the ground voltage of each phase of the distribution line, line voltage calculation means for calculating the line voltage of each phase from the detection output of the ground voltage detection means, and from the output of the ground voltage detection means. Zero-sequence voltage detection means for detecting the zero-sequence voltage of the distribution line, multiplication means for multiplying the output of the line voltage detection means and the output of the zero-sequence voltage detection means, and a filter for extracting a DC component from the output of the multiplication means. a delay means for delaying the output of the filter means for a certain period of time; a hold means for holding and outputting the output of the delay means when the hold command is inputted by a hold command; and outputting the output of the delay means as it is by a hold release command; deviation calculating means for outputting the deviation between the output of the holding means and the output of the holding means; accident signal generating means for generating an accident signal when the output of the deviation calculating means exceeds a set level; A change width detection device comprising a hold command means that outputs a hold command while the signal is being generated, continues to generate the hold command for a certain period of time when the generation of the accident signal is stopped, and then outputs a hold release command. 5. A gate means is provided between the hold command means of each phase and the hold command means for outputting a signal according to the logical sum of the input signals to the hold means, and the output of the hold command means of each phase is connected to the own gate means. 5. The variation width detection device according to claim 1, wherein the variation width detection device is connected to the input of the gate means of the other phase. 6. The variation width detection device according to claim 1, 2, 3 or 4, wherein a bandpass filter is used as the delay means. 7. Claim 2, 4, or 5, further comprising a hold release command means for monitoring the occurrence of an accident signal and forcibly outputting a hold release command to the hold command means when the occurrence of the accident signal continues for a set time or longer. 6. The change width detection device according to 6. 8. The accident signal generation means includes a level comparator that generates an accident signal when the output of the deviation calculation means exceeds a set positive level, and a level comparator that generates an accident signal when the output of the deviation calculation means exceeds a set negative level. 8. The change range detection device according to claim 1, further comprising a level comparator that generates the change width.