JP7592997B2 - Earth fault relay, earth fault cause estimation method, program, and estimation standard generation method - Google Patents

Description

This disclosure relates to a ground fault relay, a method for estimating the cause of a ground fault, a program, and a method for generating an estimation criterion.

Patent Document 1 discloses a ground fault factor estimation device that includes a data acquisition unit that acquires zero-phase data that indicates the temporal change in the zero-phase voltage or current in a power distribution line, a determination unit that determines the ground fault period in which a ground fault occurs based on the zero-phase data, and an estimation unit that estimates the ground fault factor for each predetermined period included in the ground fault period based on the classification result obtained by inputting the zero-phase data corresponding to the ground fault period into a trained model.

JP 2019-208317 A

This disclosure provides a device and method that can estimate the cause of a ground fault in a consumer facility that receives power supply from a distribution line with a simple configuration.

A ground fault relay according to one aspect of the present disclosure includes a ground fault detection unit that detects a ground fault in a customer facility based on a zero-phase current, a control unit that opens a switch between the power system and the customer facility when a ground fault is detected, a data extraction unit that extracts current data indicating a time change in the zero-phase current in an analysis period of a predetermined length based on the timing at which the ground fault is detected by the ground fault detection unit, an estimation unit that estimates whether the cause of the ground fault is cable deterioration in the customer facility or other factors based on the waveform of the current data, and an output unit that outputs the estimation result of the estimation unit.

The ground fault relay may further include a feature calculation unit that calculates features of the waveform of the current data, and the estimation unit may estimate whether the cause of the ground fault is cable deterioration or other factors based on the features.

The ground fault relay may further include a normalization unit that normalizes the current data to generate normalized data so that the maximum and minimum values of the zero-phase current are constant, and the feature calculation unit may calculate the feature based on the normalized data.

The feature calculation unit calculates a first feature representing the magnitude of variation in the zero-phase current based on the normalized data, and the estimation unit estimates based on the first feature whether the waveform of the current data belongs to a candidate group in which steady periods and impulse-like fluctuation periods alternately repeat, and when it is estimated that the waveform of the current data belongs to the candidate group, the feature calculation unit further calculates a second feature representing the fluctuation range of the zero-phase current in the fluctuation period based on the normalized data, and the estimation unit may further estimate based on the second feature whether the cause of the ground fault is cable deterioration or other.

A method for estimating the cause of an earth fault according to another aspect of the present disclosure includes extracting current data indicating a time change in zero-phase current in an analysis period of a predetermined length from an earth fault relay having an earth fault detection unit that detects the occurrence of an earth fault based on a zero-phase current and a control unit that opens a switch between the power system and the customer equipment when the occurrence of a earth fault is detected, based on the timing at which the earth fault detection unit detects an earth fault, estimating whether the cause of the earth fault is cable deterioration in the customer equipment or something else based on the waveform of the current data, and outputting the estimated result.

A program according to yet another aspect of the present disclosure causes an apparatus to execute a method for estimating the cause of an earth fault, the method including: extracting current data indicating a time change in zero-phase current in an analysis period of a predetermined length from an earth fault relay having an earth fault detection unit that detects the occurrence of an earth fault based on a zero-phase current and a control unit that opens a switch between the power system and the consumer equipment when the occurrence of a earth fault is detected, based on the timing at which the earth fault detection unit detects an earth fault; estimating whether the cause of the earth fault is cable deterioration in the consumer equipment or something else, based on the waveform of the current data; and outputting the estimated result.

A method for generating an estimation criterion according to yet another aspect of the present disclosure includes extracting current data indicating a time change in zero-phase current during a predetermined analysis period based on the timing at which the ground fault detection unit detects a ground fault from a simulated relay having a ground fault detection unit that detects the occurrence of a simulated ground fault in the simulated equipment based on the zero-phase current and a control unit that opens a simulated switch between the power system and the simulated equipment when the occurrence of a simulated ground fault is detected, calculating a feature value of the waveform of the current data, storing records that associate known causes of the simulated ground fault with the feature value, and generating an estimation criterion based on the stored records for estimating whether the cause of the simulated ground fault is cable deterioration in the simulated equipment or something else based on the waveform of the current data.

The estimation criterion generating method further includes normalizing the current data so that the maximum and minimum values of the zero-phase current are constant to generate normalized data, and calculating the feature value includes calculating a first feature value representing the magnitude of variation in the zero-phase current based on the normalized data, storing the record includes storing a first record that associates known causes of the simulated earth fault with the first feature value, and generating the estimation criterion includes storing a first estimation criterion for estimating, based on the first feature value, whether the waveform of the current data belongs to a candidate group in which steady periods and impulse-like fluctuation periods alternately repeat. , generating a first record based on the accumulated first record, calculating the feature value further includes calculating a second feature value representing a fluctuation range of the zero-phase current in a fluctuation period of the current data belonging to the candidate group based on the normalized data, storing the records further includes storing a second record in which a known cause of the simulated earth fault is associated with the second feature value, and generating an estimation criterion may further include generating a second estimation criterion based on the accumulated second record for estimating whether the cause of the simulated earth fault is cable deterioration or other based on the second feature value.

A ground fault relay according to yet another aspect of the present disclosure may include a ground fault detection unit that detects a ground fault in a consumer equipment facility based on a zero-phase current, a control unit that opens a switch between the power system and the consumer equipment when a ground fault is detected, a data extraction unit that extracts current data indicating a time change in the zero-phase current in an analysis period of a predetermined length based on the timing at which the ground fault detection unit detects the ground fault, a normalization unit that normalizes the current data based on the maximum absolute value of the zero-phase current in the current data to generate normalized data, a feature calculation unit that calculates a feature of the waveform of the current data based on the normalized data, an estimation unit that estimates whether the cause of the ground fault is cable deterioration in the consumer equipment facility or other factors based on the feature, and an output unit that outputs the estimation result of the estimation unit.

The feature calculation unit calculates a first feature representing the magnitude of variation in the zero-phase current based on the normalized data, and the estimation unit estimates based on the first feature whether the waveform of the current data belongs to a candidate group in which steady periods and impulse-like fluctuation periods alternately repeat, and when it is estimated that the waveform of the current data belongs to the candidate group, the feature calculation unit further calculates a second feature representing the bias of the zero-phase current in the fluctuation period relative to the median value of the current data based on the normalized data, and the estimation unit may further estimate based on the second feature whether the cause of the ground fault is cable deterioration or other.

A method for estimating the cause of an earth fault according to yet another aspect of the present disclosure includes extracting current data indicating a time change in zero-phase current in an analysis period of a predetermined length from an earth fault relay having an earth fault detection unit that detects the occurrence of an earth fault based on a zero-phase current and a control unit that opens a switch between the power system and the consumer equipment when the occurrence of a earth fault is detected, based on the timing at which the earth fault detection unit detects an earth fault; normalizing the current data based on the maximum absolute value of the zero-phase current in the current data to generate normalized data; calculating a feature value of the waveform of the current data based on the normalized data; estimating whether the cause of the earth fault is cable deterioration in the consumer equipment or something else based on the feature value; and outputting the estimated result.

A program according to yet another aspect of the present disclosure causes an apparatus to execute a method for estimating the cause of a ground fault, the method including: extracting current data indicating a time change in zero-phase current in an analysis period of a predetermined length based on the timing at which the ground fault detection unit detects a ground fault from a ground fault relay having a ground fault detection unit that detects the occurrence of a ground fault based on a zero-phase current and a control unit that opens a switch between the power system and the consumer equipment when a ground fault is detected; normalizing the current data based on the maximum absolute value of the zero-phase current in the current data to generate normalized data; calculating a feature value of the waveform of the current data based on the normalized data; estimating whether the cause of the ground fault is cable deterioration in the consumer equipment or something else based on the feature value; and outputting the estimated result.

An estimation criterion generating method according to yet another aspect of the present disclosure includes: extracting current data indicating a time change in zero-phase current in an analysis period of a predetermined length from a simulated relay having a ground fault detection unit that detects the occurrence of a simulated ground fault in the simulated equipment based on the zero-phase current, and a control unit that opens a simulated switch between the power system and the simulated equipment when the occurrence of a simulated ground fault is detected, based on the timing at which the ground fault detection unit detects a ground fault; normalizing the current data based on the maximum absolute value of the zero-phase current in the current data to generate normalized data; calculating a feature value of the waveform of the current data based on the normalized data; storing records that associate known causes of the simulated ground fault with the feature value; and generating an estimation criterion based on the stored records, for estimating whether the cause of the simulated ground fault is cable deterioration in the simulated equipment or other, based on the feature value.

According to this disclosure, it is possible to estimate the cause of a ground fault in a consumer facility that receives power supply from a distribution line using a simple configuration.

1 is a schematic diagram showing a schematic configuration of a ground fault cause estimation system; FIG. 2 is a schematic diagram showing an example of wiring of customer equipment. FIG. 2 is a block diagram illustrating a functional configuration of a ground fault relay. 11 is a graph illustrating normalized data before and after limit processing. 4 is a graph illustrating an example of a waveform of a zero-phase current in a state in which a ground fault occurs. 11 is a graph illustrating a second feature amount; 11 is a graph illustrating a second estimation criterion. FIG. 2 is a block diagram showing a functional configuration of an estimation reference generating device. FIG. 2 is a block diagram illustrating an example of a hardware configuration of a ground fault relay, a simulation relay, and an estimated reference generating device. 4 is a flowchart illustrating a procedure for breaking the ground fault simulation facility. 1 is a flowchart illustrating a procedure for generating an estimation criterion. 4 is a flowchart illustrating a procedure for estimating a cause of a ground fault. 13 is a graph showing a modified example of the second feature amount. 13 is a graph showing a modified example of the second estimation criterion.

The following describes the embodiments in detail with reference to the drawings. In the description, the same elements or elements having the same functions are given the same reference numerals, and duplicate descriptions are omitted.

[Earth fault cause estimation system]
The ground fault cause estimation system 1 shown in Fig. 1 is a system for estimating the cause of a ground fault in a customer facility 30 based on a current waveform in a state in which a ground fault has occurred in the customer facility 30. The ground fault here also includes a micro-ground fault in which insulation resistance has decreased. A specific example of the customer facility 30 is a high-voltage customer facility that receives power at 6600V from a power grid 90.

Between the line of the customer equipment 30 and the high-voltage line 91, the customer equipment 30 has a switch 11 and a ground fault relay 12. The switch 11 is provided between the high-voltage line 91 of the power system 90 and the line within the customer equipment 30. When the ground fault relay 12 detects a ground fault based on information on the zero-phase current and zero-phase voltage flowing through the switch 11, the switch 11 opens to separate the customer equipment 30 from the high-voltage line 91. The ground fault cause estimation system 1 estimates the cause of the ground fault in the customer equipment 30 based on information on the current acquired by the ground fault relay 12 to detect the ground fault.

As shown in FIG. 2, the power supplied from the high-voltage line 91 to the customer facility 30 via the switch 11 (hereinafter referred to as "customer power") is conducted to a cubicle 33 or the like by a cable 31 wired in a conduit 32 buried underground. The customer power may also be conducted to the cubicle 33 or the like by an electric wire 34 wired in the air. The electric wire 34 is supported by an insulating insulator 35.

Specific examples of causes of earth faults that may occur within the customer equipment 30 include deterioration of the cable 31, gap discharge, cracks in the insulator 35, contamination of the insulator 35, metal contact with the electric wire 34, and bird and animal contact with the electric wire 34. When a ground fault occurs within the customer equipment 30, the earth fault cause estimation system 1 estimates whether the cause is deterioration of the cable 31 (hereinafter referred to as "cable deterioration") or something else.

As shown in FIG. 1, the earth fault factor estimation system 1 includes an earth fault factor estimation device 13 and an estimation reference generation device 24. The earth fault factor estimation device 13 and the estimation reference generation device 24 are connected via a network line 80. The network line 80 may be a local area network or a wide area network (e.g., the Internet). The earth fault factor estimation device 13 and the estimation reference generation device 24 may be connected by a communication cable without the network line 80, or may be connected by short-distance wireless communication. The earth fault factor estimation device 13 estimates whether the cause of the earth fault is cable deterioration in the customer facility 30 or other factors based on the current information acquired by the earth fault relay 12 to detect the earth fault.

In FIG. 1, the earth fault factor estimation device 13 is incorporated in the earth fault relay 12, but this is not necessarily limited to this. The earth fault factor estimation device 13 may be incorporated in a terminal device (e.g., a tablet computer, a notebook computer, or a mobile terminal such as a smartphone) that can communicate with the earth fault relay 12. The earth fault factor estimation device 13 may also be incorporated in a server device (e.g., a server device on the cloud) that can communicate with the earth fault relay 12.

The estimation criteria generating device 24 generates an estimation criterion for the cause of a ground fault by the ground fault cause estimating device 13 based on data acquired in the ground fault simulation facility 20. For example, the estimation criteria generating device 24 generates an estimation criterion for estimating whether the cause of the ground fault is cable deterioration in the customer facility 30 or something else. The ground fault simulation facility 20 has an artificial ground fault generating device 21, a simulated switch 22, and a simulated relay 23.

The artificial ground fault generator 21 is a device that artificially generates a ground fault due to multiple types of factors assumed in the consumer equipment 30. The simulated switch 22 is provided between the high-voltage line 91 of the power system 90 and the line of the artificial ground fault generator 21. When the simulated relay 23 detects a ground fault based on information on the current flowing through the simulated switch 22, it opens the simulated switch 22 to separate the artificial ground fault generator 21 from the high-voltage line 91. The simulated switch 22 may be a manual switch. In this case, the artificial ground fault generator 21 may have an ammeter that measures the current flowing through the simulated switch 22 instead of the simulated relay 23. Below, the configuration of the ground fault relay 12 including the ground fault factor estimation device 13 and the configuration of the estimation reference generation device 24 are illustrated in detail.

(Earth fault relay)
The earth fault relay 12 including the earth fault cause estimation device 13 is configured to detect an earth fault in the customer equipment 30 based on the zero-phase current, and when a ground fault is detected, open a switch 11 between the power system 90 and the customer equipment 30, based on the timing when the earth fault is detected, extract current data indicating the time change of the zero-phase current over an analysis period of a predetermined length, based on the waveform of the current data, estimate whether the cause of the earth fault is cable deterioration in the customer equipment 30 or other cause, and output the estimation result.

Figure 3 is a block diagram illustrating the functional configuration of the ground fault relay 12. As shown in Figure 3, the ground fault relay 12 has, as its functional configuration (hereinafter referred to as "functional block"), a current detection unit 111, a data storage unit 112, a ground fault detection unit 113, a control unit 114, and a ground fault factor estimation device 13.

The current detection unit 111 detects the zero-phase current value flowing through the switch 11 based on a signal from a current sensor 195 (described later with reference to FIG. 9) or the like provided in or near the switch 11. The data storage unit 112 stores the zero-phase current values detected by the current detection unit 111 in a time series. The earth fault detection unit 113 detects an earth fault in the consumer equipment based on the time series zero-phase current values stored by the data storage unit 112. For example, the earth fault detection unit 113 detects an earth fault when the time series zero-phase current value in a predetermined period (hereinafter referred to as "current data for earth fault detection") exceeds a predetermined level.

When a ground fault is detected by the ground fault detection unit 113, the control unit 114 opens the switch 11. For example, the control unit 114 opens the switch 11 by supplying power to the coil of the switch 11 or by stopping the supply of power to the coil of the switch 11. This causes the customer equipment 30 to be disconnected from the power grid 90.

The earth fault factor estimation device 13 extracts current data indicating the time change of the zero-phase current in an analysis period of a predetermined length based on the timing when the switch 11 is opened, estimates whether the cause of the earth fault is cable deterioration in the customer equipment 30 or other factors based on the waveform of the current data, and outputs the estimation result. For example, the earth fault factor estimation device 13 has, as more detailed functional blocks, a current data extraction unit 121, a normalization unit 122, a feature calculation unit 123, an estimation criterion acquisition unit 124, an estimation criterion storage unit 125, an estimation unit 126, and an output unit 127.

The current data extraction unit 121 (data extraction unit) extracts current data indicating the time change of the zero-phase current in an analysis period of a predetermined length from the data accumulation unit 112 based on the timing at which the ground fault detection unit 113 detects a ground fault. For example, the current data extraction unit 121 extracts from the data accumulation unit 112 a time series of zero-phase current values (hereinafter referred to as "current data for factor estimation") in an analysis period including the timing at which the ground fault detection unit 113 detects a ground fault. The current data for factor estimation may be the same as the current data for ground fault detection described above.

The normalization unit 122 generates normalized data by normalizing the current data for factor estimation so that the maximum and minimum values of the zero-phase current are constant. As an example, the normalization unit 122 determines the maximum and minimum values of the zero-phase current values in the current data for factor estimation, and generates normalized data by dividing the difference between each zero-phase current value and the minimum value by the maximum and minimum values. In the normalized data generated by this example, the minimum value is zero and the maximum value is one. The method of generating normalized data can be changed as appropriate so that the minimum and maximum values are the desired values.

The feature amount calculation unit 123 calculates feature amounts of the waveform of the current data for factor estimation. The feature amount is a numerical value calculated by performing a predetermined operation on the zero-phase current value of the analysis period. The feature amount may be a vector represented by a combination of multiple numerical values. The feature amount calculation unit 123 may calculate the feature amount based on normalized data. As long as a feature amount suitable for estimating the cause of a ground fault can be calculated, there is no particular limit to the method of calculating the feature amount. For example, the feature amount calculation unit 123 may calculate the feature amount by performing statistical processing on the zero-phase current value of the analysis period, or may calculate the feature amount by performing frequency analysis such as a Fourier transform on the zero-phase current value of the analysis period.

The estimation criterion acquisition unit 124 acquires, from the estimation criterion generation device 24, an estimation criterion for estimating whether the cause of the ground fault is cable deterioration in the customer equipment 30 or something else, based on the current data for cause estimation. The estimation criterion storage unit 125 stores the estimation criterion acquired by the estimation criterion acquisition unit 124.

The estimation unit 126 estimates whether the cause of the ground fault is cable deterioration in the customer equipment 30 or something else based on the waveform of the current data for cause estimation. For example, the estimation unit 126 estimates whether the cause of the ground fault is cable deterioration in the customer equipment 30 or something else based on the feature calculated by the feature calculation unit 123. As an example, the estimation unit 126 estimates whether the cause of the ground fault is cable deterioration in the customer equipment 30 or something else based on whether the feature calculated by the feature calculation unit 123 satisfies the estimation criterion stored in the estimation criterion memory unit 125.

A specific example of the estimation criterion is a threshold value for the feature. If the feature is a vector, the estimation criterion may be a boundary in a vector space. The boundary may be defined as a function or as discrete point sequence data. The estimation criterion may be a neural network that outputs an output vector indicating whether the cause of the ground fault is cable deterioration or something else in response to an input vector. In this case, the current data itself for estimating the cause, or the normalized data itself, may be the input vector.

The output unit 127 outputs the estimation result of the estimation unit 126. For example, the output unit 127 outputs data for notifying the estimation result of the estimation unit 126 to a user interface capable of notifying information by image display, audio playback, etc. A specific example of a user interface is the display device 197 described below.

Specific examples of the calculation of features by the feature calculation unit 123 and the estimation of ground fault factors by the estimation unit 126 are shown below. The feature calculation unit 123 calculates a first feature representing the magnitude of variation in the zero-phase current based on the normalized data. For example, the feature calculation unit 123 calculates the first feature based on the standard deviation of the normalized data. The feature calculation unit 123 may calculate the standard deviation of the normalized data itself as the first feature, or may calculate the first feature by performing a further operation on the standard deviation (for example, multiplying it by a predetermined magnification). In addition, the feature calculation unit 123 may perform limit processing on the normalized data to generate second normalized data, and calculate the first feature based on the second normalized data.

Figure 4 (a) is a graph showing normalized data before limit processing. Figure 4 (b) and (c) are graphs showing examples of second normalized data after limit processing. As shown in Figure 4, the second normalized data is data from the normalized data that exists within a range from a predetermined lower limit value to an upper limit value. The upper limit value is, for example, a value obtained by adding a predetermined value to the average value of the normalized data (average value AVE in Figure 4 (a)), and the lower limit value is a value obtained by subtracting a predetermined value from the average value of the normalized data. Note that the first feature value may be an integral value of the absolute value of the difference between the second normalized data and the average value (for example, the area of the hatched portion in Figure 4 (c)).

The estimation unit 126 estimates whether the waveform of the current data for factor estimation belongs to a candidate group in which steady periods and impulse-like fluctuation periods alternately repeat based on the first feature. The steady period is a period in which the fluctuation of the zero-phase current value is substantially constant. Substantially constant means, for example, that the fluctuation of the zero-phase current value in the normalized data is within a predetermined micro-fluctuation range (range R1 in FIG. 6). The micro-fluctuation range is, for example, 10% or less of the difference between the maximum value and the minimum value, and may be 5% or less, or 1% or less.

The impulse-like fluctuation period is a period (period P1 in FIG. 6) in which the zero-phase current value substantially fluctuates over a period that is relatively short compared to the steady-state period (period P2 in FIG. 6). Substantially fluctuating means, for example, fluctuating beyond the above-mentioned minute fluctuation range. The length of the impulse-like fluctuation period is 50% or less of the length of the steady-state period, and may be 20% or less, or may be 10% or less.

Figure 5 is a graph illustrating the waveform of a zero-phase current when a ground fault occurs. Figure 5 (a) is a current waveform when a ground fault occurs due to cable deterioration. Figure 5 (b) is a current waveform when a ground fault occurs due to gap discharge. Figure 5 (c) is a current waveform when a ground fault occurs due to insulator cracking. Figure 5 (d) is a current waveform when a ground fault occurs due to insulator contamination. Figure 5 (e) is a current waveform when a ground fault occurs due to metal contact. Figure 5 (f) is a current waveform when a ground fault occurs due to bird and animal contact.

As shown in Figure 5, when a ground fault occurs due to cable deterioration or gap discharge, the waveform of the zero-phase current is a waveform in which steady periods and impulse-like fluctuating periods alternate (hereinafter referred to as an "impulse-like waveform"). In contrast, when a ground fault occurs due to insulator cracking, insulator contamination, metal contact, or contact with birds and animals, the waveform of the zero-phase current is a waveform that is relatively close to a sine wave (hereinafter referred to as a "sine-wave-like waveform").

The magnitude of variation in normalized data is significantly different between an impulse-shaped waveform such as (a) or (b) in FIG. 5 and a sinusoidal waveform such as (c) to (f) in FIG. 5. Therefore, based on the first feature, it is possible to appropriately determine whether the waveform of the current data for factor estimation belongs to a candidate group that includes current data of cable deterioration and current data of gap discharge.

When the waveform of the current data is estimated to belong to the candidate group, the feature calculation unit 123 further calculates a second feature representing the fluctuation range of the zero-phase current in the fluctuation period based on the normalized data. For example, the feature calculation unit 123 calculates the fluctuation range of the normalized data in any of the fluctuation periods as the second feature. For example, as shown in FIG. 6, the feature calculation unit 123 may calculate the fluctuation range W1 in the fluctuation period in which the normalized data is the maximum value (hereinafter referred to as the "maximum-based fluctuation range") as the second feature. The feature calculation unit 123 may calculate the fluctuation range W2 in the fluctuation period in which the normalized data is the minimum value (hereinafter referred to as the "minimum-based fluctuation range") as the second feature. The feature calculation unit 123 may calculate a vector that is a combination of the maximum-based fluctuation range W1 and the minimum-based fluctuation range W2 as the second feature.

The estimation unit 126 further estimates whether the cause of the ground fault is cable deterioration or something else based on the second feature. As shown in FIG. 5(a), in the case of cable deterioration, the zero-phase current value tends to change significantly mainly to either the positive or negative side in one fluctuation period, with little change to the other side. In contrast, in the case of gap discharge, the zero-phase current value tends to change to both the positive and negative sides in one fluctuation period. For this reason, the fluctuation range of the normalized data in a fluctuation period differs greatly between cable deterioration and gap discharge.

Figure 7 is a graph illustrating the distribution of the second feature calculated as the vector. The horizontal axis of this graph represents the magnitude of the fluctuation width W1 based on the maximum value, and the horizontal axis of this graph represents the magnitude of the fluctuation width W2 based on the minimum value. The ◇ marks represent second feature calculated based on the normalized data of cable deterioration, and the O marks represent second feature calculated based on the normalized data of gap discharge. As shown in Figure 7, the distribution of the second feature is clearly different between cable deterioration and gap discharge. Therefore, based on the second feature, it is possible to appropriately determine whether the waveform of the current data for factor estimation is a waveform of cable deterioration or a waveform of gap discharge.

As exemplified above, when the estimation unit 126 performs estimation based on the first feature amount and the second feature amount, the estimation criterion acquisition unit 124 acquires the first estimation criterion and the second estimation criterion from the estimation criterion generation device 24.

The first estimation criterion is a criterion for estimating whether or not the waveform of the current data for factor estimation belongs to the candidate group based on the first feature. The first estimation criterion may be a threshold. For example, when the first feature is smaller than the first estimation criterion, the estimation unit 126 estimates that the waveform of the current data for factor estimation belongs to the candidate group, and when the first feature is larger than the first estimation criterion, the estimation unit 126 estimates that the waveform of the current data for factor estimation does not belong to the candidate group.

The second estimation criterion is a criterion for estimating whether the cause of the ground fault is cable deterioration or other, based on the second feature. When the second feature is a single numerical value, the second estimation criterion may be a threshold value. For example, when the second feature is smaller than the second estimation criterion, the estimation unit 126 estimates that the cause of the ground fault is cable deterioration, and when the second feature is larger than the second estimation criterion, the estimation unit 126 estimates that the cause of the ground fault is other (gap discharge). When the second feature is the above-mentioned vector, the second estimation criterion may be a boundary (for example, the boundary PL in FIG. 7) between the distribution area of the second feature of cable deterioration and the distribution area of the second feature of other (gap discharge).

(Estimation standard generation device)
The estimation reference generating device 24 extracts current data indicating a time change of a zero-phase current in an analysis period of a predetermined length from the simulated relay 23 based on a timing when the simulated earth fault is detected by the simulated relay 23; Calculating a feature value of the current data, storing a feature value record in which the feature value and a known cause of the simulated earth fault are associated with each other, and determining whether the cause of the simulated earth fault is a ground fault based on the waveform of the current data. The system is configured to generate an estimation criterion for estimating whether the cause is cable deterioration in the fault simulation facility 20 or something else based on the accumulated feature amount record.

Figure 8 is a block diagram showing the functional configuration of the simulated relay 23 and the estimation reference generating device 24. The simulated relay 23 has, as functional blocks, a current detection unit 211, a data storage unit 212, a ground fault detection unit 213, and a control unit 214.

The current detection unit 211 detects the zero-phase current value flowing through the simulated switch 22 based on a signal from a current sensor (not shown) or the like provided in or near the simulated switch 22. The data accumulation unit 212 accumulates the zero-phase current values detected by the current detection unit 211 in a chronological order.

The ground fault detection unit 213 detects a simulated ground fault in the ground fault simulation equipment 20 based on the time-series zero-phase current values stored by the data storage unit 212. For example, the ground fault detection unit 213 detects a simulated ground fault when the time-series zero-phase current values in a predetermined period (hereinafter referred to as "current data for simulated ground fault detection") exceed a predetermined level.

When a ground fault is detected by the ground fault detection unit 213, the control unit 214 opens the simulated switch 22. For example, the control unit 214 opens the simulated switch 22 by supplying power to the coil of the simulated switch 22 or by stopping the supply of power to the coil of the simulated switch 22. This causes the ground fault simulation equipment 20 to be disconnected from the power system 90.

The estimation criterion generating device 24 has, as functional blocks, a current data extraction unit 221, a normalization unit 222, a feature calculation unit 223, a factor information acquisition unit 224, a record accumulation unit 225, a learning data storage unit 226, an estimation criterion generating unit 227, an estimation criterion storage unit 228, and an estimation criterion output unit 229.

The current data extraction unit 221 extracts current data indicating the time change of the zero-phase current in an analysis period of a predetermined length based on the timing when the ground fault detection unit 213 detects the simulated ground fault. For example, the current data extraction unit 221 extracts a time series of zero-phase current values (hereinafter referred to as "current data for feature calculation") in the analysis period including the timing when the ground fault detection unit 213 detects the simulated ground fault from the data accumulation unit 212. The current data for feature calculation may be the same as the current data for simulated ground fault detection described above.

The normalization unit 222 normalizes the current data for calculating the feature quantity so that the maximum and minimum values of the zero-phase current are constant, and generates normalized data. The normalization method is the same as the normalization method by the normalization unit 122 described above.

The feature amount calculation unit 223 calculates feature amounts of the waveform of the current data for feature amount calculation. The feature amount calculation unit 223 may calculate the feature amount based on the normalized data generated by the normalization unit 222. The method of calculating the feature amount by the feature amount calculation unit 223 is the same as the method of calculating the feature amount by the feature amount calculation unit 123 described above.

The factor information acquisition unit 224 acquires factor information indicating known factors of the simulated ground fault based on operator input (e.g., input to the input device 296 described below). The record accumulation unit 225 accumulates in the learning data storage unit 226 a feature record that associates the factors indicated by the factor information acquired by the factor information acquisition unit 224 with the features calculated by the feature calculation unit 223.

The estimation criterion generation unit 227 generates an estimation criterion based on the accumulated feature records to estimate whether the cause of the simulated earth fault is cable deterioration in the earth fault simulation equipment 20 or something else, based on the waveform of the current data for feature calculation. The estimation criterion memory unit 228 stores the estimation criterion generated by the estimation criterion generation unit 227. The estimation criterion output unit 229 outputs the estimation criterion stored in the estimation criterion memory unit 228 to the earth fault relay 12. This estimation criterion is acquired by the estimation criterion acquisition unit 124 described above.

The estimation criterion generating unit 227 may be configured to generate the above-mentioned first estimation criterion and second estimation criterion. In this case, the feature calculation unit 223 calculates the above-mentioned first feature based on the normalized data generated by the normalization unit 222. The record accumulation unit 225 accumulates a first record in which the factor indicated by the factor information acquired by the factor information acquisition unit 224 is associated with the first feature calculated by the feature calculation unit 223 in the learning data storage unit 226.

The estimation criterion generating unit 227 generates a first estimation criterion based on the accumulated first records for estimating whether or not the waveform of the current data for feature calculation belongs to the candidate group based on the first feature. For example, the estimation criterion generating unit 227 generates a threshold value that is the boundary between the first record group associated with cable deterioration or gap discharge and the first record group associated with other factors as the first estimation criterion.

The feature calculation unit 223 further calculates the second feature based on the normalized data generated by the normalization unit 222 for the current data belonging to the candidate group. The record accumulation unit 225 further accumulates a second record in the learning data storage unit 226, in which the factor indicated by the factor information acquired by the factor information acquisition unit 224 is associated with the second feature calculated by the feature calculation unit 223.

The estimation criterion generating unit 227 generates a second estimation criterion based on the accumulated second records for estimating whether the cause of the simulated ground fault is cable deterioration or something else based on the second feature. For example, the estimation criterion generating unit 227 generates a threshold value that is the boundary between the second record group associated with cable deterioration and the second record group associated with gap discharge as the second estimation criterion. When the second feature is the above-mentioned vector, the estimation criterion generating unit 227 may generate the boundary between the second record group associated with cable deterioration and the second record group associated with gap discharge using a support vector machine.

The estimation criterion generating unit 227 may generate the above-mentioned neural network as the estimation criterion. In this case, the estimation criterion is generated by machine learning using the accumulated feature records as training data.

Figure 9 is a block diagram illustrating the hardware configuration of the ground fault relay 12, the simulation relay 23, and the estimation reference generating device 24. The ground fault relay 12 is a computer with a communication function and has a circuit 190. The circuit 190 includes a processor 191, a memory 192, a storage 193, a communication port 194, a current sensor 195, a drive circuit 196, a display device 197, and an input device 198.

The storage 193 has a computer-readable storage medium such as a non-volatile semiconductor memory. The storage 193 stores a program that causes the ground fault relay 12 to detect a ground fault in the customer equipment 30 based on the zero-phase current, open the switch 11 between the power system 90 and the customer equipment 30 when a ground fault is detected, extract current data indicating a time change in the zero-phase current in a predetermined analysis period based on the timing at which the ground fault is detected, estimate whether the cause of the ground fault is cable deterioration in the customer equipment 30 or other factors based on the waveform of the current data, and output the estimation result. For example, the storage 193 stores a program for configuring each of the above-mentioned functional blocks in the ground fault relay 12.

The memory 192 temporarily stores the program loaded from the storage medium of the storage 193 and the calculation results by the processor 191. The processor 191 configures each functional block of the earth fault relay 12 by executing the above program in cooperation with the memory 192. The communication port 194 performs information communication with the estimation reference generating device 24 according to a command from the processor 191. The current sensor 195 detects the current flowing through the switch 11 according to a command from the processor 191. The drive circuit 196 opens the switch 11 according to a command from the processor 191. The display device 197 and the input device 198 function as a user interface of the earth fault relay 12. The display device 197 includes, for example, a liquid crystal monitor, and is used to display information to the user. The input device 198 is, for example, a keyboard, and acquires information input by the user. The display device 197 and the input device 198 may be integrated as a so-called touch panel.

The simulated relay 23 is a computer with communication capabilities and has a circuit 280. The circuit 280 includes a processor 281, a memory 282, a storage 283, a communication port 284, a current sensor 285, a drive circuit 286, a display device 287, and an input device 288.

The storage 283 has a computer-readable storage medium, such as a non-volatile semiconductor memory. The storage 283 stores a program that causes the simulated relay 23 to detect a simulated earth fault in the earth fault simulation equipment 20 based on the zero-phase current, and to open the simulated switch 22 between the power system 90 and the earth fault simulation equipment 20 when a simulated earth fault is detected. For example, the storage 283 stores a program that causes the simulated relay 23 to configure each of the above-mentioned functional blocks.

The memory 282 temporarily stores the program loaded from the storage medium of the storage 283 and the calculation results by the processor 281. The processor 281 configures each functional block of the simulated relay 23 by executing the above program in cooperation with the memory 282. The communication port 284 performs information communication with the estimation reference generating device 24 according to a command from the processor 281. The current sensor 285 detects the current flowing through the switch 11 according to a command from the processor 281. The drive circuit 286 opens the switch 11 according to a command from the processor 281. The display device 287 and the input device 288 function as a user interface for the earth fault relay 12. The display device 287 includes, for example, a liquid crystal monitor, and is used to display information to the user. The input device 288 is, for example, a keyboard, and acquires information input by the user. The display device 287 and the input device 288 may be integrated as a so-called touch panel.

The estimation criteria generating device 24 is a computer with a communication function and has a circuit 290. The circuit 290 includes a processor 291, a memory 292, a storage 293, a communication port 294, a display device 295, and an input device 296.

The storage 293 has a computer-readable storage medium such as a non-volatile semiconductor memory. The storage 293 stores a program for causing the estimation criterion generating device 24 to execute the following operations: extracting current data indicating a time change in the zero-phase current in an analysis period of a predetermined length from the simulated relay 23 based on the timing at which the simulated earth fault is detected by the simulated relay 23; calculating a feature value of the current data; storing a feature value record that associates known causes of the simulated earth fault with the feature value; and generating, based on the waveform of the current data and the stored feature value record, an estimation criterion for estimating whether the cause of the simulated earth fault is cable deterioration in the earth fault simulation equipment 20 or other causes.

The memory 292 temporarily stores the program loaded from the storage medium of the storage 293 and the calculation results by the processor 291. The processor 291 configures each functional block of the estimation criteria generating device 24 by executing the above program in cooperation with the memory 292. The communication port 294 communicates information between the simulation relay 23 and the earth fault relay 12 according to instructions from the processor 291. The display device 295 and the input device 296 function as a user interface for the earth fault relay 12. The display device 295 includes, for example, an LCD monitor, and is used to display information to the user. The input device 296 is, for example, a keyboard, and acquires information input by the user. The display device 295 and the input device 296 may be integrated as a so-called touch panel.

[Procedure for estimating earth fault cause]
As an example of a method for estimating the cause of a ground fault, a procedure for estimating the cause of a ground fault executed by the ground fault relay 12 will be illustrated. This procedure includes detecting a ground fault in the customer facility 30 based on the zero-phase current, opening the switch 11 between the power system 90 and the customer facility 30 when the ground fault is detected, extracting current data indicating a time change in the zero-phase current in an analysis period of a predetermined length based on the timing at which the ground fault was detected, estimating whether the cause of the ground fault is cable deterioration in the customer facility 30 or other factors based on the waveform of the current data, and outputting the estimation result.

As illustrated in FIG. 10, the ground fault relay 12 first executes steps S01, S02, and S03. In step S01, the current detection unit 111 detects the zero-phase current value flowing through the switch 11. In step S02, the current detection unit 111 adds the zero-phase current value to the data storage unit 112. In step S03, the ground fault detection unit 113 checks whether or not there is a ground fault in the customer equipment 30 based on the current data for ground fault detection stored in the data storage unit 112.

If it is determined in step S03 that there is no ground fault, the ground fault relay 12 returns the process to step S01. Thereafter, the detection and accumulation of the zero-phase current value and the confirmation of the presence or absence of a ground fault are repeated until a ground fault is detected in step S03.

If it is determined in step S03 that there is a ground fault, the ground fault relay 12 executes steps S04, S05, S06, S07, and S08. In step S04, the control unit 114 opens the switch 11 to disconnect the customer equipment 30 from the power grid 90. In step S05, the current data extraction unit 121 extracts current data for the above-mentioned cause estimation from the data storage unit 112 based on the timing when the ground fault detection unit 113 detects the ground fault.

In step S06, the normalization unit 122 normalizes the current data for factor estimation so that the maximum and minimum values of the zero-phase current are constant, generating normalized data. In step S07, the feature calculation unit 123 calculates the first feature representing the magnitude of variation in the zero-phase current based on the normalized data. In step S08, the estimation unit 126 checks whether the waveform of the current data for factor estimation belongs to the candidate group based on the first feature and the first estimation criterion. For example, the estimation unit 126 checks whether the first feature is smaller than the first estimation criterion.

If it is determined in step S08 that the waveform of the current data for factor estimation belongs to the candidate group, the earth fault relay 12 executes steps S11 and S12. In step S11, the feature calculation unit 123 further calculates a second feature representing the fluctuation range of the zero-phase current in the above-mentioned fluctuation period based on the normalized data. In step S12, the estimation unit 126 checks whether the cause of the earth fault is cable deterioration based on the second feature and the second estimation criterion. For example, the estimation unit 126 checks whether the second feature is smaller than the second estimation criterion.

If it is determined in step S12 that the cause of the ground fault is cable deterioration, the ground fault relay 12 executes step S13. In step S13, the output unit 127 outputs, as the estimation result of the estimation unit 126, that the cause of the ground fault is cable deterioration.

If it is determined in step S08 that the waveform of the current data for factor estimation does not belong to the candidate group, and if it is determined in step S12 that the cause of the ground fault is not cable deterioration, the ground fault relay 12 executes step S14. In step S14, the output unit 127 outputs, as the estimation result of the estimation unit 126, that the cause of the ground fault is other (other than cable deterioration). This completes the ground fault factor estimation procedure.

[Procedure for generating estimation criteria]
As an example of the estimation reference generating method, a procedure for breaking the ground fault simulation facility 20 executed by the simulation relay 23 and a procedure for estimating the cause of a ground fault executed by the estimation reference generating device 24 are illustrated.

(Procedure for shutting off earth fault simulation equipment)
11, the simulated relay 23 first executes steps S21, S22, and S23. In step S21, the current detection unit 211 detects the zero-phase current value flowing through the simulated switch 22. In step S22, the current detection unit 211 adds the zero-phase current value to the data storage unit 212. In step S23, the ground fault detection unit 213 checks whether or not a simulated ground fault exists in the ground fault simulation facility 20, based on the current data for the simulated ground fault detection stored in the data storage unit 212.

If it is determined in step S23 that there is no simulated earth fault, the simulator 23 returns the process to step S21. Thereafter, the simulator 23 repeats the detection and accumulation of the zero-phase current value and the confirmation of the presence or absence of a simulated earth fault until a simulated earth fault is detected in step S23.

If it is determined in step S23 that a simulated earth fault exists, the simulated relay 23 executes step S24. In step S24, the control unit 214 opens the simulated switch 22 to disconnect the earth fault simulation equipment 20 from the power system 90. This completes the disconnection procedure for the earth fault simulation equipment 20. In order to accumulate the above feature records in the estimation reference generation device 24, the earth fault simulation equipment 20 repeatedly generates a simulated earth fault using a known factor and causes the simulated relay 23 to execute the above procedure.

(Procedure for generating estimation criteria)
This procedure includes extracting current data indicating the time change of the zero-phase current in an analysis period of a predetermined length from the simulated relay 23 based on the timing at which the simulated earth fault is detected by the simulated relay 23, calculating features of the current data, accumulating a feature record that associates known causes of the simulated earth fault with the features, and generating, based on the waveform of the current data, an estimation criterion for estimating whether the cause of the simulated earth fault is cable deterioration in the ground fault simulation equipment 20 or other, based on the accumulated feature record.

As shown in FIG. 12, the estimation reference generating device 24 first executes steps S31, S32, S33, S34, S35, and S36. In step S31, the current data extracting unit 221 waits for the ground fault detection unit 213 to detect a simulated ground fault. In step S32, the current data extracting unit 221 extracts current data for calculating the above-mentioned feature amount from the data storage unit 212 based on the timing when the ground fault detection unit 213 detects the simulated ground fault. In step S33, the normalizing unit 222 normalizes the current data for calculating the feature amount so that the maximum and minimum values of the zero-phase current are constant values, thereby generating normalized data. In step S34, the feature amount calculating unit 223 calculates the above-mentioned first feature amount based on the normalized data generated by the normalizing unit 222.

In step S35, the factor information acquisition unit 224 acquires factor information indicating known factors of the simulated earth fault based on the operator's input. In step S36, the feature calculation unit 223 checks whether the waveform of the current data for feature calculation belongs to the above-mentioned candidate group based on the factor information. For example, if the cause of the simulated earth fault is cable deterioration or gap discharge, the feature calculation unit 223 determines that the waveform of the current data belongs to the candidate group, and if the cause of the simulated earth fault is neither cable deterioration nor gap discharge, the feature calculation unit 223 determines that the waveform of the current data does not belong to the candidate group.

If it is determined in step S36 that the waveform of the current data for feature calculation belongs to the candidate group, the estimation reference generating device 24 executes steps S37 and S38. In step S37, the feature calculation unit 223 calculates the second feature based on the normalized data generated by the normalization unit 222. In step S38, the record accumulation unit 225 adds to the learning data storage unit 226 a first record in which the factor indicated by the factor information acquired by the factor information acquisition unit 224 is associated with the first feature calculated by the feature calculation unit 223, and a second record in which the factor is associated with the second feature calculated by the feature calculation unit 223.

The record accumulation unit 225 may add one record that associates a factor, a first characteristic amount, and a second characteristic amount to the learning data storage unit 226. This one record associates a factor with the first characteristic amount and associates a factor with the second characteristic amount, so that this one record includes the first record and the second record.

If it is determined in step S36 that the waveform of the current data for feature calculation does not belong to the candidate group, the estimation reference generating device 24 executes step S38 without executing step S37. In this case, the record accumulation unit 225 adds the first record to the learning data storage unit 226.

Next, the estimation criterion generation device 24 executes step S41. In step S41, the estimation criterion generation unit 227 checks whether the number of records stored in the learning data storage unit 226 has reached a predetermined number.

If it is determined in step S41 that the number of records has not reached the predetermined number, the estimation criteria generating device 24 returns the process to step S31. Thereafter, the extraction of current data for feature calculation, the calculation of features, the acquisition of factor information, and the addition of feature records are repeated until the number of records stored in the learning data storage unit 226 reaches the predetermined number.

If it is determined in step S41 that the number of records has reached the predetermined number, the estimation criterion generation device 24 executes steps S42 and S43. In step S42, the estimation criterion generation unit 227 generates an estimation criterion based on the feature records stored in the learning data storage unit 226, and overwrites the estimation criterion in the estimation criterion storage unit 228. For example, the estimation criterion generation unit 227 calculates a first estimation criterion based on a first record stored in the learning data storage unit 226, and calculates a second estimation criterion based on a second record stored in the learning data storage unit 226. In step S43, the estimation criterion output unit 229 outputs the estimation criterion overwritten in the estimation criterion storage unit 228 to the estimation criterion acquisition unit 124. The estimation criterion acquisition unit 124 acquires the estimation criterion output from the estimation criterion output unit 229, and overwrites the estimation criterion in the estimation criterion storage unit 125. This completes the estimation criterion generation procedure.

[Effects of this embodiment]
As described above, the earth fault relay 12 includes an earth fault detection unit 113 that detects an earth fault in the customer equipment 30 based on the zero-phase current, a control unit 114 that opens the switch 11 between the power system 90 and the customer equipment 30 when a earth fault is detected, a current data extraction unit 121 that extracts current data indicating the time change of the zero-phase current over an analysis period of a predetermined length based on the timing at which the earth fault detection unit 113 detected the earth fault, an estimation unit 126 that estimates whether the cause of the earth fault is cable deterioration in the customer equipment 30 or other factors based on the waveform of the current data, and an output unit 127 that outputs the estimation result of the estimation unit 126.

This earth fault relay 12 makes it possible to easily extract current data for an analysis period suitable for estimating the cause of an earth fault based on the timing at which the switch 11 is opened. In addition, the waveform of the zero-phase current when an earth fault occurs due to cable deterioration has prominent characteristics compared to the waveform of the zero-phase current when an earth fault occurs due to other factors. Therefore, by estimating whether the cause of the earth fault is cable deterioration or something else, estimation can be made using simple calculations. Therefore, the cause of the earth fault in the customer equipment 30 can be estimated with a simple configuration.

In addition, within the customer equipment 30, ground faults can occur due to various factors, such as cable deterioration, gap discharge, insulator cracking, and contact with birds and animals, but the ease of finding the location of a ground fault varies greatly between cable deterioration and other factors. In addition, the complexity of the work required to restore from a ground fault also varies greatly between cable deterioration and other factors. For this reason, within the customer equipment 30, it is useful to simply estimate whether the cause of the ground fault is cable deterioration or other factors.

The earth fault relay 12 further includes a feature calculation unit 123 that calculates features of the waveform of the current data, and the estimation unit 126 may estimate whether the cause of the earth fault is cable deterioration or something else based on the features. In this case, the cause of the earth fault can be more easily estimated by quantifying the features of the waveform as features.

The earth fault relay 12 may further include a normalization unit 122 that normalizes the current data to generate normalized data so that the maximum and minimum values of the zero-phase current are constant, and the feature calculation unit 123 may calculate the feature based on the normalized data. In this case, by making the magnitude of the amplitude of the zero-phase current a constant value, it becomes possible to more appropriately compare the waveforms of the current data.

The feature calculation unit 123 calculates a first feature representing the magnitude of variation in the zero-phase current based on the normalized data, and the estimation unit 126 estimates based on the first feature whether the waveform of the current data belongs to a candidate group in which steady periods and impulse-like fluctuation periods alternately repeat, and when it is estimated that the waveform of the current data belongs to the candidate group, the feature calculation unit 123 further calculates a second feature representing the fluctuation range of the zero-phase current in the fluctuation period based on the normalized data, and the estimation unit 126 may further estimate based on the second feature whether the cause of the ground fault is cable deterioration or other.

The waveform of the zero-phase current when a ground fault occurs can be broadly divided into a candidate group in which steady periods and impulse-like fluctuation periods alternate, and others. Whether the waveform of the normalized data belongs to the candidate group or others can be easily determined based on the magnitude of the variation in the zero-phase current. The candidate group can include current data of cable deterioration and current data of gap discharge.

In the case of cable deterioration, the zero-phase current tends to change significantly to either the positive or negative side during one fluctuation period, with little change to the other side. In contrast, in the case of gap discharge, the zero-phase current value tends to change to both the positive and negative sides during one fluctuation period. For this reason, it is easy to determine whether the waveform of normalized data belonging to a candidate group is a waveform of cable deterioration or a waveform of gap discharge based on the fluctuation range of the zero-phase current during the fluctuation period.

Therefore, by estimating whether the current data belongs to a candidate group based on the first feature value representing the magnitude of variation in the zero-phase current, and estimating whether the current data belonging to the candidate group is current data due to cable deterioration based on the first feature value representing the fluctuation range of the zero-phase current in the fluctuation period, it is possible to more appropriately estimate whether the cause of the ground fault is cable deterioration or something else.

[Modifications]
In the above embodiment, the normalization unit 122 normalizes the current data for factor estimation so that the maximum and minimum values of the zero-phase current are constant to generate normalized data, but the method of normalizing the current data is not limited to this. For example, the normalization unit 122 may normalize the current data using the maximum absolute value of the zero-phase current in the current data as a reference to generate normalized data. For example, the normalization unit 122 generates normalized data by dividing each zero-phase current value in the current data by the maximum absolute value. Hereinafter, the value obtained by dividing the zero-phase current value by the maximum absolute value is referred to as the "normalized current value."

As an example, when the maximum absolute value of the positive zero-phase current value (hereinafter referred to as the "maximum in the positive direction") is greater than the maximum absolute value of the negative zero-phase current value (hereinafter referred to as the "maximum in the negative direction"), the normalization unit 122 calculates the normalized current value by dividing each zero-phase current value in the current data by the maximum value in the positive direction. When the maximum value in the negative direction is greater than the maximum value in the positive direction, the normalization unit 122 calculates the normalized current value by dividing each zero-phase current value in the current data by the maximum value in the negative direction. The normalization unit 122 may adjust the range of the normalized current value by multiplying by a predetermined gain, adding a predetermined constant, etc.

Depending on how the ground fault occurs, current data may be biased toward the positive side (current data in which zero-phase current occurs mainly on the positive side and almost no zero-phase current occurs on the negative side) or current data may be biased toward the negative side (current data in which zero-phase current occurs mainly on the negative side and almost no zero-phase current occurs on the positive side). In such cases, if the current data is normalized so that the maximum and minimum values of the zero-phase current are constant, normalized data that properly represents the bias toward the positive side or the negative side cannot be obtained. In contrast, the above normalization method using the maximum absolute value of the zero-phase current as a reference allows normalized data that properly represents the bias toward the positive side or the negative side to be obtained.

When the normalization unit 122 generates normalized data using a method that uses the maximum absolute value of the zero-phase current as a reference, the normalization unit 222 similarly generates normalized data using a method that uses the maximum absolute value of the zero-phase current as a reference.

In the above embodiment, an example was shown in which the feature calculation unit 123 calculates the second feature representing the fluctuation range of the zero-phase current in the fluctuation period based on the normalized data. As described above, in cable deterioration, in one fluctuation period, the zero-phase current value tends to change largely to either the positive side or the negative side, and the change to the other side tends to be small. In contrast, in gap discharge, the zero-phase current value tends to change to both the positive side and the negative side in one fluctuation period. That is, the degree of bias of the zero-phase current in the fluctuation period with respect to the median value of the current data (hereinafter simply referred to as "bias of the zero-phase current") is significantly different between cable deterioration and gap discharge. Note that the median value of the current data is the median value of the zero-phase current value in the entire current data. In cable deterioration, the bias of the zero-phase current is larger than in gap discharge. The fluctuation range of the zero-phase current in the fluctuation period correlates with the bias of the zero-phase current. For example, the greater the degree of bias of the zero-phase current, the smaller the fluctuation range of the zero-phase current. Therefore, the second feature value representing the fluctuation range of the zero-phase current can be said to be a type of quantity representing the bias of the zero-phase current. The second feature value needs to be at least a quantity representing the bias of the zero-phase current, and does not necessarily have to be a quantity representing the fluctuation range of the zero-phase current.

For example, the feature calculation unit 123 may calculate the difference between the positive fluctuation level of the zero-phase current during the fluctuation period (hereinafter referred to as the "positive fluctuation level") and the negative fluctuation level of the zero-phase current during the fluctuation period (hereinafter referred to as the "negative fluctuation level") as the second feature based on the normalized data. For example, the feature calculation unit 123 calculates the positive fluctuation level by integrating the difference between a normalized current value greater than the median of the normalized data and the median of the normalized data over time within the fluctuation period, and calculates the negative fluctuation level by integrating the difference between the median of the normalized data and a normalized current value smaller than the median of the normalized data over time within the fluctuation period. Note that the median of the normalized data is the median of the normalized current values in the entire normalized data. The feature calculation unit 123 may determine the difference between the maximum value of the normalized current value during the fluctuation period and the median of the normalized data as the positive fluctuation level, and the difference between the median of the normalized data and the minimum value of the normalized current value during the fluctuation period as the negative fluctuation level.

For example, as shown in FIG. 13, the feature calculation unit 123 may calculate a positive fluctuation level (e.g., the area of the illustrated region A1) and a negative fluctuation level (e.g., the area of the illustrated region A2) during a fluctuation period in which the normalized current value is the maximum value in the entire normalized data, and calculate the absolute value of the difference between them (hereinafter referred to as the "maximum-based bias level") as the second feature. The feature calculation unit 123 may calculate a positive fluctuation level (e.g., the area of the illustrated region A11) and a negative fluctuation level (e.g., the area of the illustrated region A12) during a fluctuation period in which the normalized current value is the minimum value in the entire normalized data, and calculate the absolute value of the difference between them (hereinafter referred to as the "minimum-based bias level") as the second feature. The feature calculation unit 123 may calculate a vector that is a combination of the maximum-based bias level and the minimum-based bias level as the second feature.

Figure 14 is a graph illustrating the distribution of the second feature calculated as the vector. The horizontal axis of this graph represents the bias level based on the maximum value, and the horizontal axis of this graph represents the bias level based on the minimum value. The ◇ marks represent second feature calculated based on the normalized data of cable deterioration, and the O marks represent second feature calculated based on the normalized data of gap discharge. As shown in Figure 14, the distribution of the second feature is clearly different between cable deterioration and gap discharge. Therefore, based on the second feature, it is possible to appropriately determine whether the waveform of the current data for factor estimation is a waveform of cable deterioration or a waveform of gap discharge.

In this way, when the feature calculation unit 123 calculates the bias level as the second feature, the feature calculation unit 223 also calculates the second feature based on the bias level. Therefore, the second estimation criterion calculated by the estimation criterion generation unit 227 is an estimation criterion based on the bias level (for example, boundary PL2 in FIG. 14). When the second feature is larger than the second estimation criterion, the estimation unit 126 estimates that the cause of the ground fault is cable deterioration, and when the second feature is smaller than the second estimation criterion, the estimation unit 126 estimates that the cause of the ground fault is other (gap discharge).

Although the embodiments have been described above, the present disclosure is not necessarily limited to the above-described embodiments, and various modifications are possible without departing from the spirit of the present disclosure.

11...switch, 12...earth fault relay, 22...simulated switch, 23...simulated relay, 30...customer equipment, 90...power system, 113...earth fault detection unit, 114...control unit, 121...current data extraction unit (data extraction unit), 122...normalization unit, 123...feature amount calculation unit, 126...estimation unit, 127...output unit.

Claims (6)

a ground fault detection unit that detects a ground fault in the customer facility based on the zero-phase current;
a control unit that opens a switch between the power grid and the customer facility when the ground fault is detected;
a data extraction unit that extracts current data indicating a time change of the zero-phase current in an analysis period of a predetermined length based on a timing at which the ground fault is detected by the ground fault detection unit;
a normalization unit that normalizes the current data to generate normalized data so that the maximum and minimum values of the zero-phase current are constant;
a feature amount calculation unit that calculates a feature amount of the waveform of the current data based on the normalized data;
an estimation unit that estimates whether a cause of the ground fault is cable deterioration in the customer facility or other causes based on the feature amount;
an output unit that outputs an estimation result of the estimation unit;
The feature amount calculation unit is
calculating a first characteristic amount representing a magnitude of variation in the zero-phase current based on the normalized data;
calculating a second feature amount representing a fluctuation range of the zero-phase current based on the normalized data;
The estimation unit is
estimating, based on the first feature amount, whether or not the waveform of the current data belongs to a candidate group in which a steady period and an impulse-like fluctuation period alternately repeat;
a ground fault relay that estimates whether the cause of the ground fault is cable deterioration or something else based on whether the waveform of the current data belongs to the candidate group and the second feature amount. a ground fault detection unit that detects a ground fault in the customer facility based on the zero-phase current;
a control unit that opens a switch between the power grid and the customer facility when the ground fault is detected;
a data extraction unit that extracts current data indicating a time change of the zero-phase current in an analysis period of a predetermined length based on a timing at which the ground fault is detected by the ground fault detection unit;
a normalization unit that normalizes the current data to generate normalized data so that the maximum and minimum values of the zero-phase current are constant;
a feature amount calculation unit that calculates a feature amount of the waveform of the current data based on the normalized data;
an estimation unit that estimates whether a cause of the ground fault is cable deterioration in the customer facility or other causes based on the feature amount;
an output unit that outputs an estimation result of the estimation unit;
The feature calculation unit calculates a first feature representing a magnitude of variation in the zero-phase current based on the normalized data;
the estimation unit estimates, based on the first feature amount, whether or not a waveform of the current data belongs to a candidate group in which a steady period and an impulse-like fluctuation period alternately repeat;
the feature amount calculation unit further calculates, when the waveform of the current data is estimated to belong to the candidate group, a second feature amount that represents a fluctuation range of the zero-phase current in the fluctuation period based on the normalized data;
The estimation unit further estimates whether a cause of the ground fault is cable deterioration or another cause based on the second feature amount. extracting current data indicating a time change of the zero-phase current in an analysis period of a predetermined length from a simulated relay having a ground fault detection unit that detects the occurrence of a simulated ground fault in the simulated equipment based on a zero-phase current and a control unit that opens a simulated switch between the power system and the simulated equipment when the occurrence of the simulated ground fault is detected, based on a timing at which the ground fault detection unit detects a ground fault;
normalizing the current data so that a maximum value and a minimum value of the zero-phase current become constant values to generate normalized data;
calculating a first characteristic amount representing a magnitude of variation in the zero-phase current based on the normalized data;
accumulating a first record in which a known cause of the simulated ground fault is associated with the first characteristic amount;
generating a first estimation criterion based on the accumulated first record for estimating, based on the first feature amount, whether or not the waveform of the current data belongs to a candidate group in which a steady period and an impulse-like fluctuation period alternately repeat;
calculating a second feature amount representing a fluctuation range of the zero-phase current during the fluctuation period of the current data belonging to the candidate group based on the normalized data;
accumulating a second record in which a known cause of the simulated ground fault is associated with the second feature amount;
generating, based on the accumulated second record, a second estimation criterion for estimating whether a cause of the simulated ground fault is cable deterioration in the simulated facility or something else based on the second feature. a ground fault detection unit that detects a ground fault in the customer facility based on the zero-phase current;
a control unit that opens a switch between the power grid and the customer facility when the ground fault is detected;
a data extraction unit that extracts current data indicating a time change of the zero-phase current in an analysis period of a predetermined length based on a timing at which the ground fault is detected by the ground fault detection unit;
a normalization unit that normalizes the current data based on a maximum value of the absolute value of the zero-phase current in the current data to generate normalized data;
a feature amount calculation unit that calculates a feature amount of a waveform of the current data based on the normalized data;
an estimation unit that estimates whether a cause of the ground fault is cable deterioration in the customer facility or other causes based on the feature amount;
an output unit that outputs an estimation result of the estimation unit;
The feature amount calculation unit
calculating a first characteristic amount representing a magnitude of variation in the zero-phase current based on the normalized data;
calculating a second feature amount representing a deviation of the zero-phase current with respect to a median value of the current data based on the normalized data;
The estimation unit is
estimating, based on the first feature amount, whether or not the waveform of the current data belongs to a candidate group in which a steady period and an impulse-like fluctuation period alternately repeat;
a ground fault relay that estimates whether the cause of the ground fault is cable deterioration or something else based on whether the waveform of the current data belongs to the candidate group and the second feature amount. a ground fault detection unit that detects a ground fault in the customer facility based on the zero-phase current;
a control unit that opens a switch between the power grid and the customer facility when the ground fault is detected;
a data extraction unit that extracts current data indicating a time change of the zero-phase current in an analysis period of a predetermined length based on a timing at which the ground fault is detected by the ground fault detection unit;
a normalization unit that normalizes the current data based on a maximum value of the absolute value of the zero-phase current in the current data to generate normalized data;
a feature amount calculation unit that calculates a feature amount of a waveform of the current data based on the normalized data;
an estimation unit that estimates whether a cause of the ground fault is cable deterioration in the customer facility or other causes based on the feature amount;
an output unit that outputs an estimation result of the estimation unit;
The feature calculation unit calculates a first feature representing a magnitude of variation in the zero-phase current based on the normalized data;
the estimation unit estimates, based on the first feature amount, whether or not a waveform of the current data belongs to a candidate group in which a steady period and an impulse-like fluctuation period alternately repeat;
when it is estimated that the waveform of the current data belongs to the candidate group, the feature calculation unit further calculates a second feature representing a bias of the zero-phase current in the fluctuation period with respect to a median value of the current data based on the normalized data;
The estimation unit further estimates whether a cause of the ground fault is cable deterioration or another cause based on the second feature amount. extracting, from a ground fault relay including a ground fault detection unit that detects the occurrence of a ground fault based on a zero-phase current and a control unit that opens a switch between the power system and a consumer facility when the occurrence of the ground fault is detected, current data that indicates a time change of the zero-phase current in an analysis period of a predetermined length based on a timing at which the ground fault detection unit detects a ground fault;
normalizing the current data based on a maximum value of an absolute value of the zero-phase current in the current data to generate normalized data;
Calculating a feature amount of a waveform of the current data based on the normalized data;
estimating whether a cause of the ground fault is cable deterioration in the customer facility or other causes based on the feature amount;
and outputting the estimated result.
Calculating a feature amount of the waveform of the current data based on the normalized data,
calculating a first characteristic amount representing a magnitude of variation in the zero-phase current based on the normalized data;
calculating a second feature amount representing a fluctuation range of the zero-phase current based on the normalized data;
Including,
Estimating whether the cause of the ground fault is cable deterioration in the customer facility or other causes based on the feature amount includes:
estimating, based on the first feature amount, whether or not the waveform of the current data belongs to a candidate group in which a steady period and an impulse-like fluctuation period alternately repeat;
estimating whether a cause of the ground fault is deterioration of the cable or another cause based on whether a waveform of the current data belongs to the candidate group and the second feature amount;
Including , the program .

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