JPH0670448A - Method of detecting grounded phase and grounded feeder - Google Patents

Abstract

PURPOSE:To simply determine a grounded phase by detecting the polarity of the first wave of a pulse-shaped signal generated in a zero-phase voltage signal and the polarity of each-phase voltage signal at that time and by detecting a phase where the phase difference between the pulse-shaped signal and phase voltage signal is a specific value. CONSTITUTION:Phase voltage signals VA-VC, zero-phase voltage signal V0 and zero-phase current signal I0 are inputted to a multiplexer 6 via sample-and- hold circuits 1-5, A/D converted 7 successively, and inputted to the RAM10 of CPU8. The CPU8 processes data by a program which R0M9 builts in. When a ground fault occurs, the polarities of the pulse-shaped first-wave of the rise of VO and respective-phase VA-VC at that point of time are detected and compared with each other, and a phase in the position of 0-90 deg. or 180-270 deg. from the pulse-shaped signal is determined as an earth phase, displayed in an operation panel 12 and printed out 14. Also, it is notified to other ends via communication IF 15. Thus, even a self-resetting momentary earth is detected surely.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a ground fault phase detection method and a ground fault feeder detection method when an instantaneous ground fault phenomenon or a fine ground fault phenomenon occurs before a continuous accident.

[0002]

2. Description of the Related Art Conventionally, as a means for detecting an instantaneous ground fault phenomenon in, for example, a fine ground fault relay, there is a means for detecting an effective value level of a zero-phase voltage Vo. Further, even in a ground fault protection relay that protects the system from a complete ground fault, the ground fault accident determination is performed by combining the effective value of the zero phase voltage Vo with other information such as a zero phase current.

[0003]

The conventional ground fault protection relay has a zero-phase voltage V regardless of the analog or digital system.
Although the ground fault is determined based on the effective value level of o, a so-called ghost voltage may be superimposed on Vo due to a cause other than the ground fault, so that it is erroneously determined as a ground fault. There is. In addition, since the ground fault protection relay originally cuts off only the line that is operationally impaired due to the expansion of the accident when a ground fault is detected, it is possible to eliminate the accident point spontaneously such as an instantaneous ground fault. Must not break the line. For that reason, generally, a certain period of operation is provided. Further, a low-pass filter is generally provided to prevent malfunction due to noise components superimposed on the zero-phase voltage. Therefore, in the conventional ground fault protective relay, the waveform of the zero-phase voltage Vo is several cycles (0.1
.About.0.3 S) and is effective only when the effective value level exceeds a certain threshold value. Therefore, in the case where the accident phase is self-recovered within less than 1/4 cycle of the fundamental frequency like an instantaneous ground fault, the zero phase voltage V
Instantaneous ground fault cannot be detected only by o. As described above, the conventional ground fault protection relay is used only for protecting the ground fault as a continuous accident, and does not obtain maintenance information before the continuous accident.

If, for example, the insulator is cracked by several lightning strikes and water enters, an instantaneous ground fault or a fine ground fault may occur at that location. On the contrary, such a ground fault is continuously generated. The need for maintenance and inspection can be known by detecting it as a precursory phenomenon to the accident.

An object of the present invention is, in detecting a momentary ground fault phenomenon or a minute ground fault phenomenon as a precursor phenomenon leading to a continuous ground fault accident, in which phase the ground fault occurred or in which feeder the ground fault occurred. An object of the present invention is to provide a ground fault phase detection method and a ground fault feeder detection method for detecting a fault.

[0006]

A ground fault phase detecting method according to claim 1 of the present invention detects the polarity of a first wave of a pulse signal generated in a zero-phase voltage signal at the time of a ground fault, and detects the pulse signal. The polarity of each phase voltage signal at the time of occurrence is detected, and a phase in which the polarity of the detected phase voltage signal has a reverse polarity to the polarity of the pulse signal is detected as a ground fault phase.

A ground fault phase detecting method according to a second aspect of the present invention detects the polarity of the first wave of the pulse-shaped signal generated in the zero-phase voltage signal at the time of ground fault, and polarizes each phase voltage signal when the pulse-shaped signal is generated. Is detected, and the polarity of the detected phase voltage signal is opposite to the polarity of the pulse signal, and when the pulse signal is generated, 0 ° to 90 ° or 180 ° of the phase voltage signal.
It is characterized by detecting a phase of ˜270 ° as a ground fault phase.

In the ground fault phase detecting method according to a third aspect of the present invention, the product of each phase voltage signal and the zero phase voltage signal is moved and added for a fixed time, and the phase having the largest negative value is detected as the ground fault phase. It is characterized by

In the ground fault phase detecting method according to a fourth aspect of the present invention, the effective value of each phase voltage signal is obtained within a certain time range, and the phase in which the effective value at the time of occurrence of the ground fault is most reduced is detected as the ground fault phase. Characterize.

The ground fault feeder detection method according to claim 5 is
The polarity of the first wave of the pulsed zero-phase current signal generated when a ground fault occurs is detected for each feeder, and the feeder whose polarity appears opposite to that of the other feeder is detected as the ground fault feeder. .

The ground fault feeder detection method according to claim 6 is
The amount of energy inflow and outflow is calculated for each feeder by the product of zero-phase voltage and zero-phase current for the time range of 1/4 cycle or less of the fundamental wave. It is characterized in that it is detected as a feeder.

[0012]

First, FIG. 2 shows the waveform of each signal before and after the occurrence of the instantaneous ground fault. In the figure, VA, VB, and VC are phase voltage signals of A phase, B phase, and C phase, respectively, and Vo is a zero phase voltage signal. Further, Io1 to Io4 are zero-phase current signals in the first to fourth feeders. In this example, a ground fault has occurred in the B phase of the second feeder at time to.

When a ground fault occurs in the positive half cycle in the B phase, a positive voltage is generated as the zero phase voltage Vo.
On the other hand, both the A-phase voltage VA and the C-phase voltage VC have the same polarity as the rising edge of Vo. In the ground fault phase detection method according to claim 1, the polarity of the first wave of the pulse-shaped signal generated in the zero-phase voltage signal at the time of the ground fault and the polarities of the respective phase voltage signals simultaneously generated are detected, respectively. A phase having a reverse polarity to the polarity of the phase voltage signal is detected as a ground fault phase. In the example of FIG. 2, the B phase having the opposite polarity to Vo is detected as the ground fault phase.

If a ground fault occurs during a positive half cycle of both VA and VB at a timing slightly earlier than the time to shown in FIG. 2, the phase having the opposite polarity to Vo is determined as the A phase and the B phase. However, while the B phase has a ground fault in the range of the phase of 0 ° to 90 °, the A phase is not within this phase range. Generally a ground fault is 0 ° to 90 ° or 18
0 ° to 270 ° (in most cases 45 ° to 90 ° or 22
Since it occurs in a range of 5 ° to 270 °), a single phase can be detected as a ground fault phase by the above determination. In the ground fault phase detection method according to claim 2, not only the polarity determination of the zero-phase voltage signal and each phase voltage signal described above but also the phase of each phase voltage signal when the pulsed zero-phase voltage signal is generated is considered. Therefore, a single ground fault phase can be detected.

As shown in FIG. 2, with respect to the polarity of Vo, a decrease in the ground fault phase with respect to normal is generated in the opposite polarity. Therefore, if the product sum of each phase voltage signal and the zero phase voltage signal is obtained for a certain period of time before and after the occurrence of the ground fault accident, << 0 will be obtained for the accident phase. On the other hand, the sound phase does not always become positive from the relationship with the phase, but if you look only at the transient phenomenon when a ground fault occurs, the sound phase voltage signal is touched on the same polarity side as Vo. The sum of products of the phase voltage signal and the zero phase voltage signal is> 0. In the ground fault phase detection method according to the third aspect, the phase having the largest negative value is detected as the ground fault phase by performing the above calculation.

As shown in FIG. 2, the ground-fault voltage signal always has an effective value smaller than the normal effective value as compared with the sound phase signal, and the sound phase has a larger value. Claim 4
In the ground fault phase detection method according to (1), the effective value of each phase voltage signal is obtained in a certain time range, and the phase in which the effective value when the ground fault occurs is most reduced is detected as the ground fault phase.

Now, when all are viewed in the same polarity direction at the same exit point of the distribution line, if a ground fault occurs at a certain feeder, all zero-phase currents flow toward the ground fault point, so that the sound feeder is healthy. And in the accident feeder, it appears with the opposite polarity when it starts up. In the ground fault feeder detection method according to claim 5, the polarity of the first wave of the pulsed zero-phase current signal generated when a ground fault occurs is detected for each feeder, and among them, the feeder that appears in the opposite polarity to the other feeder is the ground fault. Detected as a feeder. For example, when a ground fault occurs in the second feeder F2 in the distribution line system shown in FIG. 16, a zero-phase current flows in each feeder as shown in FIG. In the example of FIG. 2, the rising polarity of Io1, Io3, and Io4 is negative, whereas the rising polarity of Io2 is positive. From this, the second feeder can be detected as a ground fault feeder.

When the inflow / outflow amount of energy is calculated for each feeder by the product of the zero-phase voltage and the zero-phase current, if the side to which the ground fault current is supplied is negative energy, only one feeder becomes negative and the other The feeder becomes positive. Moreover, it is considered that the sum of the energies of the other feeders approximates the energy of the accident feeder. Therefore, the absolute value of the accident feeder is the maximum. In the ground fault feeder detection method according to claim 6, the inflow / outflow amount of energy is obtained for each feeder by the product of the zero-phase voltage and the zero-phase current in the time range of ¼ cycle or less of the fundamental wave. The feeder with the maximum energy input is detected as the ground fault feeder.

[0019]

1 is a block diagram of a ground fault detecting device according to an embodiment of the present invention. In FIG. 1, sample and hold circuits 1 to 5 sample and hold the phase voltage signals VA, VB and VC, the zero phase voltage signal Vo and the zero phase current signal Io, respectively. The multiplexer 6 selects one of the sample hold circuits 1 to 5 according to the selection signal and outputs it to the A / D converter 7. The A / D converter 7 converts the voltage signal into digital data. The CPU 8 executes a program written in advance in the ROM 9 to perform processing for ground fault detection. The RAM 10 is used as a working area for various calculations. Operation panel 1
Reference numeral 2 sets various calculation parameters and displays the ground fault detection result via the operation panel interface 11. The printer 14 records and saves the detection result of a ground fault accident via the printer interface 13. The communication interface 15 transmits a ground fault detection result or the like to another monitoring device via a communication line or a distribution line.

Next, a processing procedure of the CPU 8 shown in FIG. 1 is shown as a flow chart in FIGS. FIG. 7 shows the processing procedure of the entire ground fault detection apparatus. First, various calculation parameters to be described later are set in n100. Subsequently, in n101, a calculation for detecting the occurrence of a ground fault is performed, and this is repeated until a ground fault occurs (n102 → n101 ...).
If a ground fault occurs, calculation for ground fault phase detection and calculation for ground fault feeder detection are performed (n103 → n10).
4). The processing of steps n101 to n104 is repeatedly executed n times (until the ground fault is detected n times). After that, the detected ground fault phase and ground fault feeder are displayed on the CRT of the operation panel.
And display it on the printer (n10
5). Then, if necessary, the calculation parameters are reset and the same process is repeated (n106 → n100 → ...
・).

FIG. 8 is a flow chart showing the processing procedure of step n101 in FIG. The process shown in FIG. 8 will be described below with reference to FIGS.

In step n1 shown in FIG. 8, the zero-phase voltage data Vo which has already been sampled and stored is read in time series and the effective value thereof is obtained. This effective value calculation formula is as follows.

[0023]

[Equation 1]

Here, N is the number of data in the range for obtaining the effective value. For example, when sampling one cycle of the fundamental frequency at 256 points, N is set to 64 points corresponding to 1/4 cycle. The calculation of the equation 1 is obtained by the movement calculation for each data.

In step n2 of FIG. 8, it is determined whether or not the obtained effective value of Vo exceeds a predetermined threshold value. If the threshold value is not exceeded, it is considered that the ground fault has not occurred, and the effective value calculation is performed again on 64 points of Vo data including the data after one point (n2 → n1). If it exceeds the threshold value, the difference filter operation is performed on the zero-phase voltage signal Vo at n3. This is a process for removing the stationary fundamental wave component and the direct current component included in the Vo signal, and subtracts one cycle of the fundamental wave data from each Vo sampling data. This calculation is expressed by the following equation.

[0026]

## EQU00002 ## Vo ^s (i) = Vo (i) -Vo (i-256) FIG. 3 is a diagram showing the effect of the differential filter calculation. Vo is the original zero-phase voltage signal before differential filtering, and Vo ^s is the zero-phase voltage signal after differential filtering. In this way, the steady fundamental wave component and the direct current component are removed, and a zero-phase voltage signal containing only a pulsed signal due to a ground fault is obtained.

Subsequently, at step n4 shown in FIG. 8, the starting point of the ground fault is detected from the zero-phase voltage signal after the differential filtering. Specifically, it is determined whether or not the condition that the change amount of the current sampling data with respect to the previous sampling data exceeds a predetermined value ΔV continues twice. For example, as shown in FIG. 5, the variation between the i-th data Vo ^s (i) and the next sampling data Vo ^s (i + 1) is ΔV.
And the next sampling data Vo ^s (i +
When the change from 2) also exceeds ΔV in the same direction, the timing of i is detected as the starting point.

Subsequently, in step n5 of FIG. 8, digital high-pass filter calculation is performed on each phase voltage signal VA, VB, VC. For example, FIR digital high-pass filtering is performed by the calculation of the following equation.

[0029]

[Equation 3]

Here, a (Z) has a cutoff frequency of 60.
A value that is 0 Hz is used. VN corresponds to any of VA, VB, and VC.

Further, in the above digital high-pass filtering, if i is the starting point, VN ^h (i-512) to VN ^h (i-512) to VN
^h (i + 256) range, VN (i
It is performed in the range of −542) to VN (i + 256).

Subsequently, in step n6 of FIG. 8, differential filtering is further performed on each phase voltage signal after high-pass filtering. As a result, the fundamental wave component slightly contained in each phase voltage after high-pass filtering is almost completely removed. Calculation method

The law is

Similar to the equation 2, the difference from the data of 256 points before, which corresponds to the data of one period before the fundamental wave, is obtained. The calculation range at this time is VN ^s (i-256) to V when i is the starting point.
A range of N ^s (i + 256), VN ^h (i-512) to VN in terms of high-pass filtered data
It is in the range of ^h (i + 256).

FIG. 4 is a diagram showing the effect of digital high-pass filtering and differential filtering on the phase voltage signal. Here, as an example, the phase voltage VB of phase B, the data VB ^h after the high-pass filtering, and differential filtering are performed. The data VB ^hs shown in FIG. In this way, the kick component included in the phase voltage signal is extracted by the high-pass filtering, and the steady fundamental wave component is substantially completely removed by the differential filtering.

Then, in step n7 of FIG. 8, data for which the digital high-pass filtering and the differential filtering have been performed on the respective phase voltage signals VA, VB, and VC are obtained.

Then, the effective value is obtained. this is

The square root of the sum of squares of each data is calculated for a certain range in the same manner as in [Equation 1]. The effective value calculation range at that time is 1 / before and after including the starting point based on the starting point previously obtained.
4 cycles.

As described above, the starting point candidate is detected and the effective value of each phase voltage at that point is obtained. Then, in n102 of FIG. 7, it is determined whether or not the kick phenomenon occurs in each phase voltage signal.

FIG. 9 shows the processing procedure of step n103 in FIG. First, the initial value 0 is substituted for the value Z representing the ambiguity of the ground fault phase determination result, and the initial value 0 is substituted for the data A, B, C representing the certainty of the ground fault phase determination result (n1
0). Then, the ground fault phase detection method according to claim 1 or 2 is applied to determine the ground fault phase from the rising polarities of the zero-phase voltage signal and the voltage signal of each phase (n11). Then claim 3
The ground fault phase detection method is applied to obtain the sum of products of the zero-phase voltage signal and the voltage signal of each phase, and the ground fault phase is determined from the polarity (n12). Further subsequently, the ground fault phase detection method according to claim 4 is applied to determine the ground fault phase from the reduction rate of the effective value of each phase voltage signal (n13). In each of the determination processes of steps n11 to n13, the variable A corresponding to the phase regarded as the ground fault phase,
Count +1 for each of B and C. After performing the processing up to n13, the phase with the maximum count value is regarded as the ground fault phase unless A = B = C = 1, and the determination result is output (n14 → n15). If the first determination result is A = B = C = 1, the data representing the ambiguity is incremented by Z and the determination processing of n13 is executed again. That is, the weight of the ground fault phase determination based on the reduction rate of the effective value of each phase voltage signal is increased to perform a comprehensive ground fault phase determination.

Next, specific procedures of the three types of ground fault phase determination processing shown in FIG. 9 are shown in FIGS. FIG. 11 shows a processing procedure of n11 in FIG. First, the rising polarity of Vo is detected, and the rising polarities of VA, VB, and VC are detected, and the phase having the rising polarity opposite to the rising polarity of Vo is counted as +1 for the ground fault phase.

For example, if Vo is +, and VA, VB, and VC are +, +, and-, respectively, C is incremented by +1. For example, if Vo is − and VA, VB, and VC are +, −, and +, respectively, +1 is counted in A and C.

FIG. 12 shows the processing procedure of n12 in FIG. First, the sum of products Vo (i) × VN (i) is calculated for the data of 1/2 cycle from the starting point i to i + 128. Here, VN is any one of VA, VB, and VC.
If one of the phases becomes negative as a result of this calculation, the phase is incremented by +1. Further, if two or more phases are negative, Z is incremented and the phase having the smallest calculated value is counted by +1.

FIG. 13 shows a processing procedure of n13 in FIG. First, as shown in FIG. 6, with respect to the phase voltage signal, the effective value XN1 of −1/2 cycle to +1/2 cycle centered on the starting point VN (i) is obtained, and the effective value XN0 for the preceding one cycle is calculated. Calculate the ratio (decrease rate). Then, +1 is counted for the phase in which the reduction rate is the maximum.

Next, the procedure for determining the ground fault feeder will be described. FIG. 10 shows the processing procedure of step n104 shown in FIG. 7. First, the initial value 0 is substituted for the data Z representing the ambiguity of the ground fault feeder determination result, and the data representing the certainty of the feeder in which the ground fault has occurred. Substitute an initial value of 0 into F0 to F4 (when determining for four feeders) (n2
0). Then, the ground fault feeder detection method of claim 5 is applied to determine the ground fault feeder from the rising polarity of the zero-phase current signal of each feeder (n21). Subsequently, the ground fault feeder detection method according to claim 6 is applied to determine the ground fault feeder based on the ground fault energy calculation of each feeder (n2).
2). If any of F0 to F4 has a count value of 2, that is, if there is a feeder that satisfies both the conditions of n21 and n22, the feeder is regarded as a ground fault feeder and the determination result is output (n23 → n25). If none of F0 to F4 reaches 2 in the first judgment by n21 and n22, the data Z representing the ambiguity of the judgment result is incremented, and the judgment by the inflow / outflow amount of energy is performed again to increase the weight. The ground fault feeder is comprehensively determined (n23 → n24 → n22).

FIG. 14 shows a processing procedure of n21 in FIG. First, an initial value of the number of samples for calculating an average value described later is substituted for N (n30). Next, the initial value 0 is assigned to each of the variable PP for counting the number of feeders in which the rising polarity of the zero-phase current is + and the variable NN for counting the feeders in which the rising polarity of the zero-phase current signal is −, and the determination is made. Initial value 1 as feeder number x to be
Is substituted (n31). Subsequently, the average value Io'x (where x is a feeder number) of the zero-phase current signal is obtained for several data (for example, sampling data for 5 times) after starting for each feeder (n32). If this calculation result is +, PP is incremented and the feeder number is stored in JP (n32 → n33). If the operation result is −, NN is incremented and the feeder number is stored in JN (n33 → n35). Then, the same process is performed for the feeders 2 to 4 (n35 → n36 →
n37 → n32 ...). If PP is 1 when the zero-phase current rising calculation is performed for four feeders, that is, if the rising polarity of the zero-phase current is only one +, then that feeder (JP) is used as a ground fault feeder.
Count one (n38 → n39). If NN is 1, that is, if there is only one feeder in which the rising polarity of the zero-phase current is −, the feeder is counted as +1 as a ground fault feeder (n40 → n41). If PP = 1 and NN = 1 are not satisfied, the number of samples N for which the average value is calculated is reduced and the same processing is performed (n42 → n43 → n31 ...
・).

If the ground fault feeder cannot be determined even when N becomes 1, Z is incremented and the process is terminated (n44).

FIG. 15 shows the processing of step n22 in FIG. First, i-127 to i + 1 where i is the starting point
The ground fault energy is calculated for each feeder in the range of 28. If the result of the calculation is negative for only one feeder, that feeder is counted as +1 for the ground fault feeder. If the calculation results of the two feeders are negative, Z is incremented and the feeder having the minimum calculation result is counted by +1.

As described above, the ground fault phase is detected by the three types of detection methods, the phase with the highest accuracy is determined as the ground fault phase by comprehensive judgment, and the two types of ground fault feeder detection methods are used. The ground fault feeder is judged by comprehensive judgment.

The determination results obtained by various detection methods may be weighted in advance to perform more accurate ground fault phase determination and ground fault feeder determination.

[0049]

According to the present invention, like the instantaneous ground fault, 1
Even in the case where the ground fault is self-recovered in less than / 4 cycle, the transient phenomenon can be caught and the ground fault phase and the ground fault feeder can be reliably detected. Further, according to the present invention, since the detection is performed from the start-up time of the ground fault, the present invention can be applied not only to the instantaneous ground fault but also to the complete ground fault.

[Brief description of drawings]

FIG. 1 is a block diagram of a ground fault detecting device according to an embodiment of the present invention, and FIG. 2 is a waveform diagram of each signal before and after occurrence of a ground fault. Figure 3
4 is a waveform diagram of the zero-phase voltage signal after the differential filter calculation, and FIG. 4 is a waveform diagram of the phase voltage signal after the digital high-pass filter calculation and the differential filter calculation. FIG. 5 is an explanatory diagram for detecting the starting point. FIG. 6 is a waveform diagram for explaining one of the ground fault phase detection methods. 7 is a flowchart showing the processing procedure of the entire ground fault detection apparatus shown in FIG. 1, and FIGS. 8, 9 and 10 are step n in FIG.
10 is a flowchart showing the processing procedures of 101, n103, and n104, respectively. 11, 12 and 1
3 is steps n11, n12 and n13 in FIG.
It is a flowchart showing the processing procedure of. 14 and 15 are flowcharts showing the processing procedure of steps n21 and n22 in FIG. FIG. 16 is a diagram showing a configuration example of a distribution line.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Masatsugu Hirose, 2109, Yashima Nishimachi, Takamatsu City, Kagawa Prefecture 8 Shikoku Research Institute, Inc. (72) Inventor Hideto Oki 47 Umezu Takaunecho, Ukyo-ku, Kyoto City Nissin Electric Co., Ltd.

Claims (6)

[Claims] 1. A polarity of a first wave of a pulse signal generated in a zero-phase voltage signal at the time of a ground fault is detected, a polarity of each phase voltage signal when the pulse signal is generated is detected, and the detected phase voltage signal is detected. A ground fault phase detection method for detecting, as a ground fault phase, a phase whose polarity is opposite to that of the pulse signal. 2. The polarity of the first wave of the pulse-shaped signal generated in the zero-phase voltage signal at the time of ground fault is detected, and the polarity of each phase voltage signal at the time of generation of the pulse-shaped signal is detected. The polarity is opposite to the polarity of the pulse signal, and the phase voltage signal is 0 to 9 when the pulse signal is generated.
A ground fault phase detection method for detecting a phase of 0 ° or 180 ° to 270 ° as a ground fault phase. 3. A ground fault phase detection method in which a product of each phase voltage signal and a zero phase voltage signal is moved and added for a fixed time, and a phase having the largest negative value is detected as a ground fault phase. 4. A ground fault phase detection method, wherein an effective value of each phase voltage signal is obtained in a fixed time range, and a phase in which the effective value when a ground fault occurs is most reduced is detected as a ground fault phase. 5. The polarity of the first wave of the pulsed zero-phase current signal generated when a ground fault occurs is detected for each feeder, and the feeder whose polarity appears opposite to that of another feeder is detected as a ground fault feeder. Ground fault feeder detection method. 6. The inflow / outflow amount of energy is calculated for each feeder by the product of the zero-phase voltage and the zero-phase current in the time range of ¼ cycle or less of the fundamental wave, and when the ground fault occurs, the energy has the maximum value in the inflow direction. A ground fault feeder detection method for detecting a feeder that takes a ground fault as a ground fault feeder.