Earth fault position estimating device and earth fault position estimating method

Abstract

A power distribution system (1) is provided with power transmission paths (12H, 12F) in which at least one current measuring instrument (15a to 15e) is disposed, and a power supply device (14) which outputs a current for measuring a zero-phase current. A zero-phase current detecting unit (22) detects the zero-phase current from current measurement results notified from the current measuring instruments (15a to 15e). When an earth fault incident occurrence detecting unit (23) detects the occurrence of an earth fault incident in the power distribution system (1) on the basis of the zero-phase current, the earth fault incident occurrence detecting unit (23) instructs the power supply device (14) to output a current. An earth fault incident occurrence point estimating unit (25) estimates an occurrence location (16) of the earth fault incident on the basis of a resonance frequency calculated from the waveform of the zero-phase current detected in accordance with the output of the current by the power supply device (14).

Description

Ground fault location estimation device and ground fault location estimation method

[0001] The present disclosure relates to a ground fault location estimation device and a ground fault location estimation method.

[0002] An electric power grid is an operational system for supplying power to consumers' power receiving equipment, and is responsible for generating, transforming, transmitting, and distributing electricity. If an accident occurs in the electric power grid, the supply of power to consumers will be cut off. Therefore, it is necessary to quickly identify the cause of the accident, the section where the accident occurred, and the location of the accident, and then carry out restoration work. Conventionally, the location of an accident has generally been identified mainly by visual inspection by track maintenance workers, but this method takes a long time to identify the location of the accident in an electric power distribution grid that has a length of several kilometers to tens of kilometers.

[0003] One type of fault that can occur in a power system is a ground fault. When a ground fault occurs, a zero-phase sequence current and a zero-phase sequence voltage are generated. Therefore, for example, Japanese Patent No. 4550464 (Patent Document 1) describes a method for detecting a ground fault by monitoring the zero-phase sequence current and the zero-phase sequence voltage.

[0004] Furthermore, Patent Document 1 describes a method of estimating a ground fault location from a resonance component included in a zero-phase current waveform. More specifically, the method describes a method of detecting resonance of a zero-phase current detected when a ground fault occurs, calculating the resonance frequency, and comparing the calculated resonance frequency with past data or the like to estimate the fault location.

[0005] Patent No. 4550464

[0006] The estimation of the ground fault location in Patent Document 1 is based on the phenomenon in which the resonant frequency of the zero-phase sequence current changes depending on the distance from the substation to the ground fault location. However, because ground faults can occur due to lightning strikes, contact with birds and animals, or trees, it is expected that the ground fault impedance will change in various ways at the moment of the ground fault occurrence. As a result, when a ground fault occurs, there is a risk that a distorted zero-phase sequence current waveform will be observed. From such a distorted zero-phase sequence current waveform, it is difficult to detect an accurate resonant frequency that reflects the distance from the ground fault location.

[0007] Therefore, with the method described in Patent Document 1, there is a concern that the accuracy of estimating the ground fault location may decrease due to the inability to derive an accurate resonant frequency.

[0008] The present disclosure has been made to solve such problems, and an object of the present disclosure is to improve the accuracy of estimating a ground fault location using a zero-phase sequence current.

[0009] According to one aspect of the present disclosure, there is provided a ground fault location estimation device for a power distribution system. The power distribution system is provided with a transmission line on which at least one current meter is installed, and a power supply device that outputs a current for measuring a zero-phase current to the transmission line. The ground fault location estimation device includes a current measurement result collection unit, a zero-phase current detection unit, a ground fault occurrence detection unit, and a ground fault occurrence point estimation unit. The current measurement result collection unit collects current measurement results notified from the current meter. The zero-phase current detection unit detects a zero-phase current in the transmission line from the current measurement results. When the ground fault occurrence detection unit detects a ground fault in the power distribution system based on the detected zero-phase current, it instructs the power supply device to output a current. The ground fault occurrence point estimation unit estimates the occurrence point of the ground fault based on the zero-phase current detected by the current measurement result collection unit and the zero-phase current detection unit in response to the output of the measured current by the power supply device. The ground fault occurrence point estimation unit calculates a resonance frequency from the waveform of the zero-phase current, and estimates the location of the occurrence point based on the calculated resonance frequency.

[0010] According to another aspect of the present disclosure, there is provided a method for estimating a location of a ground fault in a power distribution system. The power distribution system is provided with a transmission line on which at least one current meter is installed and a power supply device that outputs a current for measuring a zero-phase current to the transmission line. The method includes the steps of: determining whether a ground fault has occurred in the power distribution system based on a zero-phase current in the transmission line detected from a current measurement result notified by the current meter; instructing the power supply device to output a measurement current when a ground fault has occurred; and estimating the location of the ground fault based on the zero-phase current detected from the current measurement result notified by the current meter after the power supply device outputs the measurement current. The estimating step calculates a resonant frequency from a waveform of the zero-phase current and estimates the location of the occurrence point based on the calculated resonant frequency.

[0011] According to the present disclosure, the location of a ground fault can be estimated based on the resonant frequency of the zero-phase current generated by the current from the power supply device after the occurrence of a ground fault, rather than the zero-phase current at the time of the occurrence of a ground fault, which is a concern as it may result in a distorted current waveform, thereby improving the accuracy of estimating the location of the ground fault.

[0012] 1 is a schematic configuration diagram of a ground fault location estimation device and an entire system of a power distribution system according to a first embodiment. FIG. 1 is a conceptual diagram for explaining a zero-phase current generated when a ground fault occurs in the power distribution system shown in FIG. 1. FIG. 2 is a block diagram for explaining the configuration of a ground fault occurrence point estimation unit shown in FIG. 1. FIG. 3 is a block diagram for explaining an example configuration of a computer system for realizing the ground fault location estimation device. FIG. 4 is a flowchart for explaining an example of control processing for estimating a ground fault point by the ground fault location estimation device according to the first embodiment. FIG. 5 is a conceptual diagram for explaining an overview of correlation data. FIG. 6 is a conceptual diagram for explaining the function of a ground fault point matching unit. FIG. 7 is a schematic configuration diagram of a ground fault location estimation device and an entire system of a power distribution system according to a second embodiment. FIG. 8 is a waveform diagram schematically showing simulation results of resonant frequency components of zero-phase current generated when a measurement current is supplied from each power supply device 14 in FIG. 8. FIG. 9 is a conceptual diagram for explaining the path of a zero-phase current when a measurement current is output from a power supply device away from a ground fault point. FIG. 10 is a conceptual diagram for explaining the path of a zero-phase current when a measurement current is output from a power supply device near a ground fault point. 10 is a flowchart illustrating an example of a control process for estimating a ground fault point by a ground fault position estimation device according to a second embodiment.

[0013] Hereinafter, embodiments of the present disclosure will be described in detail with reference to the drawings. In the following, the same or corresponding parts in the drawings will be denoted by the same reference numerals, and their description will not be repeated in principle.

[0014] First Embodiment Fig. 1 is a schematic diagram of the overall system including a ground fault location estimation device 2A and a power distribution system according to a first embodiment.

[0015] As shown in FIG. 1 , when a ground fault occurs in a power distribution system 1, a ground fault position estimation device 2A estimates the position (occurrence point) of the ground fault.

[0016] The power distribution system 1 is configured so that power is supplied from a distribution substation 11 to a plurality of branched feeders 12. The plurality of feeders 12 includes a fault feeder 12F in which a ground fault has occurred and a healthy feeder 12H in which no ground fault has occurred. Note that, in this embodiment, a ground fault location estimation is described for a power distribution system 1 provided with a plurality of branched feeders 12, but the ground fault location estimation according to this embodiment can also be applied to the range of a single feeder 12 with no branching.

[0017] Each feeder 12 is assumed to be configured as a typical three-phase distribution line, but the number of phases is not limited to this. While the configuration of a fault feeder 12F is illustrated in FIG. 1 , the configuration of each feeder 12 is basically the same. Each of the multiple feeders 12 corresponds to an example of a "power transmission line."

[0018] Multiple current measuring devices 15 are installed on the fault feeder 12F, but the locations and number (one or more) of the current measuring devices 15 installed on each feeder 12 are optional. In the example of Figure 1, on the fault feeder 12F where current measuring devices 15a to 15e are installed, a ground fault has occurred at a ground fault point 16 located between current detectors 15c and 15d. In other words, the ground fault point 16 corresponds to the "point where the ground fault occurred."

[0019] Each of the current measuring devices 15a to 15e measures the current (three-phase current) flowing through the installation location. Each current measuring device 15 also has the function of storing measured data and the function of communicating with other devices. Alternatively, the current measuring device 15 may be configured as part of the functions of a detector that also has other functions, such as the function of measuring line voltage. The current measurement data Ida to Ide from the current measuring devices 15a to 15e are input to the ground fault location estimation device 2A.

[0020] A power supply device 14 is further installed in the power distribution system 1 for generating a zero-phase current after detecting the occurrence of a ground fault. The power supply device 14 has a function of outputting a current for measuring the zero-phase current (hereinafter referred to as a "measurement current") in response to an output command from the ground fault location estimation device 2A. The measurement current may be, for example, a pulse current with a period of about 5 ms to 10 ms, but is not limited to this.

[0021] The power supply device 14 may be arranged exclusively for detecting ground fault points, but it can also be configured by adding a function to an existing power supply device in the distribution system 1 to output the above-mentioned measured current in response to an output command from the ground fault location estimation device 2A.

[0022] In addition, the power supply device 14 may be provided for each feeder 12, or may be provided commonly to a plurality of feeders. In the configuration example of Figure 1, the measurement current from the power supply device 14 flows through both the faulted feeder 12F and the healthy feeder 12H.

[0023] A healthy feeder 12H without a ground fault has a ground capacitance 17 between it and the ground GND. The ground capacitance 17 represents the aggregate of the ground capacitances distributed within the healthy feeder 12H due to the distribution lines, customer equipment, cables, etc.

[0024] The ground fault location estimation device 2A includes a current measurement result collection unit 21, a zero-phase current detection unit 22, a ground fault occurrence detection unit 23, a data storage unit 24, and a ground fault occurrence point estimation unit 25. The ground fault location estimation device 2A is provided for each predetermined area (detection area) of the power distribution system 1, and uses current measurement data from each current meter 15 arranged within the detection area to identify the fault feeder 12F included in the detection area and estimate the ground fault point 16 within the fault feeder 12F. The ground fault location estimation device 2A illustrated in FIG. 1 is configured to include at least the feeder 12 corresponding to the fault feeder 12F in its detection area.

[0025] The current measurement result collecting unit 21 collects current measurement data Id from each current measuring device 15 arranged on each feeder 12 within the detection area of ​​the ground fault location estimation device 2A. In the configuration example of FIG. 1 , the current measurement result collecting unit 21 collects current measurement data Ida to Ide from current measuring devices 15a to 15e arranged on the fault feeder 12F. The zero-phase current detecting unit 22 calculates the zero-phase current Ipz at each current measuring device 15 from the current measurement value (current measurement data Id) collected by the current measurement result collecting unit 21.

[0026] 2 is a conceptual diagram for explaining the zero-phase-sequence current Ipz that occurs when a ground fault occurs in the distribution system 1. Fig. 2 shows the flow path of the zero-phase-sequence current Ipz in a configuration in which a fault feeder 12F including a ground fault point 16 and two healthy feeders 12H1 and 12H2 branch off from each other, and a grounding potential transformer (GPT) 18 for detecting the zero-phase-sequence voltage Vpaz is located near the distribution substation 11.

[0027] As shown in Fig. 2, each feeder 12 is divided into a plurality of distribution sections by switches 13, and a current meter 15 is installed in each distribution section. As described in Fig. 1, the ground fault point 16 is located between current meters 15c and 15d.

[0028] In the fault feeder 12F, the zero-phase current Ipz includes a component flowing through the fault feeder 12F and a component flowing through each of the healthy feeders 12H1 and 12H2. In the fault feeder 12F, the zero-phase current flows into the ground GND at the ground fault point 16, then passes through the earth capacitance 17a or 17b and flows back to the distribution line (fault feeder 12F). The earth capacitance 17a corresponds to the sum of the earth capacitances in the section upstream of the ground fault point 16 in the fault feeder 12F (the distribution substation 11 or power supply 14 side), and the earth capacitance 17a corresponds to the sum of the earth capacitances in the section downstream of the ground fault point 16 in the fault feeder 12F.

[0029] On the other hand, in each of the healthy feeders 12H1 and 12H2, the zero-phase current that flowed into the ground GND at the ground fault point 16 flows through the earth capacitance 17c or 17d and returns to the distribution line (healthy feeder 12H1, 12H2). The earth capacitance 17c corresponds to the sum of the earth capacitances of the entire healthy feeder 12H1, and the earth capacitance 17d corresponds to the sum of the earth capacitances of the entire healthy feeder 12H2.

[0030] Generally, the impedance of the earth capacitances 17c and 17d of the healthy feeders 12H1 and 12H2 is much smaller than the impedance of the earth fault point 16, so most of the zero-phase current Ipz flows through the faulty feeder 12F. Therefore, the magnitude of the zero-phase current measured by the current meter 15 differs between the feeders 12.

[0031] Furthermore, in the fault feeder 12F, a zero-phase sequence current flows into the ground fault point 16, and therefore the direction of the zero-phase sequence current detected by the current meters 15a to 15c arranged upstream of the ground fault point 16 differs from that detected by the current meters 15d and 15e arranged downstream of the ground fault point 16. On the other hand, in each of the healthy feeders 12H1 and 12H2, the current meters 15 detect zero-phase sequence currents in the same direction.

[0032] Therefore, in each feeder 12, it is possible to determine whether a ground fault has occurred based on at least one of the magnitude of the zero-phase current and whether the zero-phase current is in the same direction. Furthermore, in the fault feeder 12F, it is possible to determine whether a ground fault has occurred in the section between two current meters 15 that form a pair of adjacent pairs of current meters 15, each pair having opposite zero-phase current directions. In the example of Figure 2, it is possible to determine whether a ground fault has occurred in the section between current meters 15c and 15d, whose zero-phase currents flow in opposite directions. Alternatively, even in a feeder 12 with only one current meter 15, it is possible to determine whether a ground fault has occurred based on the magnitude of the zero-phase current.

[0033] It is known that the zero-phase current generates an oscillation component at a resonant frequency determined by the inductance component of the distribution line and the capacitance of the earth capacitance 17a. It is understood that this resonant frequency varies depending on the distance (distribution line length) from the current supply point (distribution substation 11 or power supply device 14) to the ground fault point 16. Therefore, as in Patent Document 1, the location of the ground fault point can be estimated by back-calculating the distance to the ground fault point 16 from the resonant frequency of the zero-phase current. When a ground fault occurs, the resonant frequencies of the zero-phase current detected at each point (current meter 15) are equivalent. Therefore, in principle, the resonant frequency can be calculated using the current measurement data Id from any current meter 15. However, as described above, because the amplitude of the zero-phase current differs between current meters 15, it is preferable to calculate the resonant frequency from the current measurement data Id from the appropriate current meter 15 (e.g., the current detector installed on the fault feeder 12F).

[0034] 1 again, the ground fault occurrence detection unit 23 determines whether a ground fault has occurred based on the direction (polarity) of the zero-phase current of each current measuring device 15 calculated by the zero-phase current detection unit 22, and when a ground fault occurs, can identify the fault feeder 12F including the ground fault point 16 from the multiple feeders 12. Furthermore, based on the polarity of the zero-phase current of each current measuring device 15 in the fault feeder 12F, it can identify the section including the ground fault point 16 (hereinafter also referred to as the "fault section") from each section having two adjacent current measuring devices 15 at both ends.

[0035] When the ground fault occurrence detection unit 23 detects the occurrence of a ground fault, it generates an output command Szc of a measurement current (e.g., a pulse current) for generating a zero-phase current to the power supply device 14. The power supply device 14 outputs the measurement current in response to the output command Szc, thereby generating a zero-phase current Ipz in the fault feeder 12F.

[0036] The zero-phase-sequence current Ipz generated by the measurement current from the power supply device 14 also contains the above-mentioned resonant frequency component, and can be detected by the zero-phase-sequence current detection unit 22 using current measurement data from the current meter 15 (for example, in the fault feeder 12F). The zero-phase-sequence current Ipz at this time is input from the zero-phase-sequence current detection unit 22 to the ground fault occurrence location estimation unit 25.

[0037] Furthermore, when the ground fault accident occurrence detection unit 23 detects the occurrence of a ground fault accident, it further outputs identification data Dfdx including information identifying the fault feeder 12F and information identifying the fault section within the fault feeder 12F. The identification data Dfdx is input from the ground fault accident occurrence detection unit 23 to the data storage unit 24 and the ground fault accident occurrence point estimation unit 25.

[0038] The data storage unit 24 stores correlation data between the distance (the length of the distribution line) from a reference point (for example, the location of the power supply device 14) to the point where a ground fault occurs and the resonance frequency when a ground fault occurs. The correlation data can be created in advance using past accident data in the distribution system 1 and / or simulation results of ground faults using a simulator.

[0039] When the specific data Dfdx is input from the ground fault occurrence detection unit 23 , that is, when a ground fault is detected, the data storage unit 24 outputs the correlation data to the ground fault occurrence location estimation unit 25 .

[0040] The correlation data may be determined in advance for each feeder 12. In this case, from the correlation data of each of the multiple feeders 12, the correlation data corresponding to the fault feeder 12F indicated by the identification data Dfdx is output from the data storage unit 24. In addition, in this embodiment, the correlation data is described as being stored in advance in the data storage unit 24, but it may also be input from outside the ground fault position estimation device 2A (such as a server) in response to the output from the ground fault occurrence detection unit 23.

[0041] 3, the ground fault occurrence location estimation unit 25 includes a frequency calculation unit 251 and a ground fault point matching unit 252. After an output command is issued to the power supply device 14, the frequency calculation unit 251 calculates the resonant frequency from the waveform of the zero-phase current Ipz calculated by the zero-phase current detection unit 22. As described in Patent Document 1, the frequency calculation unit 251 can calculate the resonant frequency by applying a fast Fourier transform (FFT) or the like to the zero-phase current waveform.

[0042] The ground fault point matching unit 252 matches the correlation data with the calculated resonant frequency to determine the estimated distance from a predetermined reference point (e.g., the power supply device 14) to the point where the ground fault occurred. The estimation result by the ground fault point matching unit 252 is output to the outside from the ground fault position estimation device 2A.

[0043] FIG. 4 is a block diagram illustrating an example of the configuration of a computer system for realizing the ground fault location estimation device 2A.

[0044] As shown in FIG. 4, the computer system 40 can have a general configuration including a display unit 41, an input unit 42, a network interface (I / F) 43, a memory 44, a CPU (Central Processing Unit) 45, an HDD (Hard Disk Drive) 46, and a bus 47.

[0045] The ground fault location estimation device 2A shown in FIG. 4 can be realized using a computer system 40 as follows.

[0046] Specifically, the function of the current measurement result collection unit 21 in Fig. 1 can be realized by a network interface (I / F) 43 in Fig. 4 and an analog-to-digital converter (A / D converter) not shown in the input unit 42. Also, the function of the data storage unit 24 can be realized by storing correlation data using a partial area of ​​the HDD 46 in Fig. 4. Alternatively, when correlation data is input from outside the ground fault location estimation device 2A, this function can be realized by the network interface 43.

[0047] Furthermore, the functions of each of the zero-phase current detection unit 22, the ground fault occurrence detection unit 23, and the ground fault occurrence location estimation unit 25 can be realized by executing a program stored in the HDD 46 or memory 44 in Figure 4 by the CPU 45 in Figure 4.

[0048] The estimation result obtained by the ground fault occurrence point estimation unit 25 can be displayed to the user using the display unit 41. Alternatively, the estimation result may be transmitted to an external device of the ground fault location estimation device 2A via the network interface 43.

[0049] Alternatively, unlike the example of FIG. 4, at least a part of the ground fault location estimation device 2A can be configured using circuits such as an FPGA (Field Programmable Gate Array) and an ASIC (Application Specific Integrated Circuit).

[0050] FIG. 5 is a flowchart illustrating an example of a control process for estimating a ground fault point by the ground fault position estimating device 2A according to the first embodiment.

[0051] As shown in Fig. 5, in step (hereinafter simply referred to as "S") 100, the ground fault location estimation device 2A determines whether or not a ground fault has occurred by the ground fault occurrence detection unit 23 based on the zero-phase-sequence current sequentially acquired by the current measurement result collection unit 21 and the zero-phase-sequence current detection unit 22. In S110, the process branches depending on the determination result in S100. Specifically, when a ground fault has been detected, a YES determination is made in S110, and the process proceeds to S120. On the other hand, when a ground fault has not been detected (a NO determination is made in S110), the process of S120 is not executed, and the processes of S100 and S110 are repeated.

[0052] In S120, the ground fault location estimation device 2A determines the feeder (fault feeder 12F) and section (fault section) where the ground fault occurred using the ground fault occurrence detection unit 23. As described above, based on the direction (or magnitude and direction) of the zero-phase current Ipz in each current meter 15, the fault feeder 12F and the section where the ground fault occurred (hereinafter also referred to as the "fault section") divided by two current meters 15 that sandwich the point where the ground fault occurred within the fault feeder 12F are identified. In S120, identification data Dfdx is generated.

[0053] In S130, the ground fault location estimation device 2A generates an output command Szc to the power supply device 14 by the ground fault occurrence detection unit 23. As a result, a measured current (e.g., pulse current) of the zero-phase current is output from the power supply device 14 to the power distribution system 1 including the ground fault point 16.

[0054] In S140, when a measurement current is supplied from the power supply device 14, the ground fault location estimation device 2A calculates the zero-phase current Ipz from the current measurement data Id in each current meter 15 using the current measurement result collection unit 21 and the zero-phase current detection unit 22.

[0055] In S150, the ground fault location estimation device 2A causes the ground fault occurrence point estimation unit 25 to acquire the zero-phase current from the zero-phase current detection unit 22, and in S160, the frequency calculation unit 251 calculates the resonance frequency frs of the zero-phase current.

[0056] In S170, the ground fault position estimation device 2A causes the ground fault occurrence point estimation unit 25 to acquire correlation data including the fault section of the fault feeder 12F from the data storage unit 24.

[0057] FIG. 6 is a conceptual diagram illustrating an overview of correlation data. As shown in FIG. 6 , the resonant frequency frs can be calculated from actual data or simulation data when a ground fault occurs at each point in the power distribution system 1. By defining a coordinate plane with the resonant frequency frs on the horizontal axis and the distance Dx from a predetermined reference point (e.g., the distribution substation 11 or the power supply device 14) to the point where the ground fault occurs on the vertical axis, characteristic points defined by the combination of the resonant frequency frs and the distance Dx from the reference point can be plotted for each point. The reference point corresponds to a source of a current that generates a zero-phase current. In the case where actual data is used, the reference point is the distribution substation 11. However, in the case where simulation data is used, the reference point can be either the distribution substation 11 or the power supply device 14 depending on the simulation conditions.

[0058] From these plotted points, a characteristic line 50 can be obtained that represents the relationship between the resonance frequency frs and the distance Dx from the reference point. In the example of Fig. 6, the characteristic line 50 is obtained by linear approximation, but the characteristic line 50 may also be obtained by approximation using a curve or an arbitrary function.

[0059] The correlation data is a group of data for expressing the characteristic line 50, and may be, for example, data indicating the coordinates (frs, Dx) at multiple points on the characteristic line 50. In this case, by interpolating or extrapolating the multiple points indicated by the correlation data, the distance Dx from the reference point for any resonant frequency frs of the zero-phase current within the expected range can be obtained.

[0060] Referring again to Figure 5, in S180, the ground fault position estimation device 2A uses the ground fault point matching unit 252 to estimate the ground fault point from the correlation data acquired in S170 and the resonant frequency of the zero-phase current calculated in S160.

[0061] 7 is a conceptual diagram illustrating the function of the ground fault point matching unit 252. As shown in Fig. 7, the ground fault point matching unit 252 can calculate an estimated distance Des (Dx = Des) from the reference point corresponding to the resonance frequency frs = fes calculated in S160 on the characteristic line 50 according to the correlation data acquired in S170. This estimated distance Des corresponds to the length of the distribution line from the reference point (e.g., the point where current is supplied by the power supply device 14) in the correlation data of Fig. 6.

[0062] The ground fault point matching unit 252 can use the topology information of the power distribution system 1 created in advance and the calculated estimated distance to determine, as an estimation result, the estimated position of the ground fault point on the power distribution system 1. For example, in the power transmission route that passes through the fault section from the power supply device 14, which is an example of a reference point indicated by the topology information, a point at a distance (length of the distribution line) = D1 from the power supply device 14 can be determined as the estimated position of the ground fault point.

[0063] Referring again to FIG. 5 , the ground fault position estimation device 2A outputs data DRfp indicating the estimation result obtained by the ground fault point matching unit 252 to the outside in S190. For example, if the ground fault position estimation device 2A is installed in a manned command center of a monitoring system, the estimated position of the ground fault point can be displayed using a display unit 41 ( FIG. 4 ), such as a display. Alternatively, if the ground fault position estimation device 2A is installed in an unmanned substation or the like, the estimation result obtained by the ground fault point matching unit 252 can be output via the network interface 43 so as to be transmitted from the ground fault position estimation device 2A to an external device, such as the device in the command center. In other words, the ground fault position estimation device 2A can be installed in any location.

[0064] As described above, the ground fault location estimation device according to the first embodiment can estimate the location of the ground fault point using the resonant frequency calculated from the waveform of the zero-phase-sequence current generated by supplying a current from the power supply device 14 to the power distribution system 1 including the ground fault point 16 after the occurrence of a ground fault, rather than the waveform of the zero-phase-sequence current obtained when the ground fault occurs. In particular, the accuracy of estimating the location of the ground fault point can be improved by calculating an accurate resonant frequency that reflects the distance (the length of the distribution line) from the power supply device 14 that supplies the measurement current to the ground fault point 16.

[0065] Embodiment 2. Fig. 8 is a schematic configuration diagram of an entire system of a ground fault location estimation device and a power distribution system according to embodiment 2. In embodiment 2, the explanation will focus on the parts that are different from embodiment 1, and therefore, the explanation of matters common to embodiment 1 will not be repeated.

[0066] 8, a power distribution system 1 to which a ground fault location estimation device 2B according to the second embodiment is applied is provided with a plurality of power supply devices 14. For example, in the example of FIG. 8, a plurality of power supply devices 14A and 14B are provided in the power distribution system 1.

[0067] The ground fault location estimation device 2B differs from the ground fault location estimation device 2B of embodiment 1 in that, when a ground fault is detected, it has the function of selecting one power supply device from multiple power supply devices 14 that outputs a current (measurement current) for measuring the zero-phase current.

[0068] In the example of Figure 8, compared to the ground fault location estimation device 2A, the ground fault location estimation device 2B has a ground fault occurrence detection unit 23 that separately generates an output command Szca for the power supply device 14A and an output command Szcb for the power supply device 14B. The output commands Szca and Szcb are selectively generated. When the output command Szca is generated, the power supply device 14A outputs a measurement current, while when the output command Szcb is generated, the power supply device 14B outputs a measurement current. The measurement current is, for example, a pulse current, as in the first embodiment.

[0069] Furthermore, with regard to the correlation data stored in the data storage unit 24, correlation data for the power supply unit 14 described in the first embodiment is prepared for each of the plurality of power supply units 14. That is, in the example of Fig. 8, individual correlation data is prepared for each of the power supply units 14A and 14B. Note that also in the second embodiment, the correlation data may be input from outside the ground fault location estimation device 2B (such as a server) in response to the output from the ground fault occurrence detection unit 23.

[0070] Furthermore, like the ground fault location estimation device 2A, the ground fault location estimation device 2B can be configured using a computer system 40 illustrated in Figure 4, or at least some of its functions can be configured using circuits such as FPGAs and ASICs.

[0071] Next, the selection of multiple power supply devices will be explained using Figures 9 to 11. Here, it is assumed that, in power distribution system 1, power supply device 14B is located near ground fault point 16, and power supply device 14A is located some distance away from ground fault point 16, as shown in Figure 8.

[0072] Fig. 9 is a waveform diagram schematically showing the simulation results of the resonant frequency component of the zero-phase current generated when a measurement current is supplied from each power supply device 14 in Fig. 8. Fig. 9 shows a waveform diagram of the resonant current component in which the fundamental wave component has been removed and only the vibration component has been extracted from the simulation results of the zero-phase current generated when a predetermined current pulse (measurement current) is output from each of power supply devices 14A and 14B under the condition that ground fault point 16 in Fig. 8 is grounded in a circuit model simulating power distribution system 1.

[0073] 9, when a resonant current waveform 101 obtained when a current pulse is output from the power supply device 14A is compared with a resonant current waveform 102 obtained when a current pulse is output from the power supply device 14B, the two have the same frequency but a difference in amplitude, with the amplitude of the resonant current waveform 102 (power supply device 14B) being smaller than the amplitude of the resonant current waveform 101 (power supply device 14B). Therefore, it can be seen that calculating the resonant frequency using the resonant current waveform 101 is easier than calculating the resonant frequency using the resonant current waveform 102, and the accuracy of calculating the resonant frequency is also improved.

[0074] FIG. 10 is a conceptual diagram illustrating the path of the zero-phase current when a current pulse (measurement current) is output from the power supply device 14A.

[0075] As shown in Figure 10, the power supply unit 14A is located upstream (towards the distribution substation 11) of the branch point of the fault feeder 12F and the healthy feeders 12H1 and 12H2, and is located relatively far from the ground fault point 16.

[0076] The zero-phase current Ipz generated by the current pulse (measurement current) output from the power supply unit 14A results in the current (Ipz1) flowing through the fault feeder 12F and the current (Ipz2, Ipz3) flowing through the healthy feeders 12H1 and 12H2 occurring in parallel, and the frequency (resonant frequency) of the vibration component changes depending on the position of the ground fault point 16.

[0077] Therefore, the zero-phase current can be considered to flow through a parallel circuit of a first impedance corresponding to each of the healthy feeders 12H1 and 12H2 from the power supply device 14A and a second impedance from the power supply device 14A to the ground fault point 16 of the fault feeder 12F.

[0078] The oscillation of the zero-phase current occurs due to the exchange of energy between the first impedance and the second impedance. Therefore, in the example of Fig. 10, it can be seen that the path length through which the zero-phase current flows is relatively long and the inductance component of the distribution line is also large.

[0079] In contrast to this, FIG. 11 shows a conceptual diagram illustrating the path of the zero-phase current when a current pulse (measurement current) is output from the power supply device 14B.

[0080] As shown in FIG. 11, the power supply device 14B is disposed near the ground fault point 16 on the fault feeder 12F.

[0081] The zero-phase current Ipz generated by the current pulse (measurement current) output from the power supply device 14B almost entirely flows into the ground fault point 16, and the inductance component of the distribution line in the path of the zero-phase current becomes very small. In this case, energy exchange between the parallel-connected impedances as shown in Figure 10 is unlikely to occur. As a result, it can be seen that resonance is less likely to occur in the case of Figure 11 than in the case of Figure 10.

[0082] As a result, as shown in FIG. 9, a simulation result is obtained in which the resonant current waveform 102 (power supply device 14A) has a larger amplitude than the resonant current waveform 101 (power supply device 14B).

[0083] It is known that the resonance sharpness (Q value) of an LC circuit depends on the inductance component L and the capacitance component C, and is proportional to √(L / C). Since the resonance sharpness increases when the inductance component of the power distribution line in the path of the zero-phase current is large, it can be understood that the calculation of the resonance frequency becomes easier and more accurate.

[0084] Therefore, when multiple power supply devices 14 are installed, it is understood that one power supply device (hereinafter also referred to as the "selected power supply device") that outputs a measurement current should be selected based on the positional relationship between each power supply device 14 and the ground fault point 16, so as to avoid using a power supply device 14 that is too close to the ground fault point 16. In the examples of Figures 8 to 11, it is understood that when a ground fault occurs in the section between current meters 15d and 15e, the measurement current should be output from power supply device 14A located farther away, rather than from nearby power supply device 14B.

[0085] 8 , as described in the first embodiment, the ground fault occurrence detection unit 23 can identify the fault feeder 12F and the fault section within the fault feeder 12F based on the direction of the zero-phase current detected by each current meter 15 of each feeder 12. Therefore, a selected power supply device can be determined in advance from the plurality of power supplies 14 for each section of each feeder 12 based on the configuration of the power distribution system 1. For example, power supply selection list data indicating the selected power supply device for each section of each feeder 12 can be stored in advance in the data storage unit 24.

[0086] Then, by referring to the power supply selection list data stored in the data storage unit 24, the ground fault accident occurrence detection unit 23 can read out selection data Dsl indicating the selected power supply device corresponding to the fault section indicated by the identification data Dfdx. The ground fault accident occurrence detection unit 23 can output an output command Szc to one of the multiple power supply devices 14 based on the selection data Dsl read out from the data storage unit 24. In the example of Figure 8, the selection data Dsl specifying the power supply device 14A is returned from the data storage unit 24 for the fault section (including the ground fault point 16) between the current meters 15d and 15e of the fault feeder 12F, and the ground fault accident occurrence detection unit 23 generates an output command Szca for the power supply device 14A.

[0087] FIG. 12 is a flowchart illustrating an example of a control process for estimating a ground fault point by the ground fault position estimating device according to the second embodiment.

[0088] As shown in Figure 12, the ground fault location estimation device 2B performs steps S100 to S120 similar to those in Figure 5, using the ground fault occurrence detection unit 23 to detect and determine a ground fault based on zero-phase current, and to determine the fault feeder 12F and the fault section when a ground fault occurs.

[0089] When the ground fault location estimation device 2B identifies the fault section in the fault feeder 12F in S120, the ground fault occurrence detection unit 23 notifies the data storage unit 24 of the determination result identifying the fault section in S210. Furthermore, in S220, the data storage unit 24 refers to the power supply selection list data described above to acquire the selection result of the power supply device 14 corresponding to the fault section. The selection result is notified from the data storage unit 24 to the ground fault occurrence detection unit 23.

[0090] In S130, the ground fault location estimation device 2B generates a measurement current output command for the power supply device 14 selected in S220. When one power supply device 14 that received the output command generated in S130 outputs the measurement current, the same processes as in S130 to S190 in FIG. 5 are executed.

[0091] In the second embodiment, as in the first embodiment, the resonant frequency is calculated based on the zero-phase current waveform generated by the measured current output from one power supply (selected power supply) (S140 to S160). Furthermore, in S170, correlation data (FIG. 5) corresponding to the power supply 14 selected in S220 is extracted, and the distance (length of the power distribution line) from a predetermined reference point (for example, the power supply 14 that generated the measured current) can be estimated from the resonant frequency, thereby estimating the point of the ground fault (S180), as in the first embodiment.

[0092] As described above, the ground fault location estimation device according to the second embodiment can select a power supply device that outputs a current for measuring the zero-phase current when a ground fault occurs, taking into consideration its positional relationship with the fault section (the length of the distribution line). This not only achieves the effects described in the first embodiment, but also improves the accuracy of detecting the resonant frequency, thereby improving the accuracy of estimating the ground fault point.

[0093] In the second embodiment, the number and locations of the multiple power supply devices 14 within the power distribution system 1 are arbitrary, but for each point within the power distribution system 1, taking into consideration the distance between each power supply device 14 (the length of the distribution line), it is possible to predetermine one power supply device to be used for estimating the ground fault point in this embodiment, corresponding to each point (for example, each section of each feeder 12).

[0094] 8 and 12 have described an example in which power source selection list data stored in advance in the data storage unit 24 is used, but the power source selection list data may be input from outside the ground fault location estimation device 2B (such as a server) in response to output from the ground fault occurrence detection unit 23. Alternatively, without using a power source selection list, information specifying the power source device 14 to be selected corresponding to the detected fault section may be input to the ground fault location estimation device 2B from outside the ground fault location estimation device 2B.

[0095] Furthermore, since the actual configuration of the power distribution system 1 is a complex combination of branches of the feeders 12 illustrated in FIGS. 1 and 8, it is difficult to strictly formulate the relationship between the resonant frequency and the length of the power distribution line. However, as described in FIG. 6, by using past accident record data and / or simulation data to prepare in advance characteristic lines 50 for each power supply path (feeder 12) in the power distribution system 1, it is possible to apply the estimation of the ground fault point described in this embodiment.

[0096] Note that the control processing for estimating the ground fault point shown in Figures 5 and 12 is merely an example, and it is possible to add, change, delete, or otherwise modify the processing as desired within the scope of achieving the same effect.

[0097] As described above, the ground fault location estimation device according to this embodiment can be provided in each predetermined area (detection area) of the power distribution system 1, and in some cases, it can also be arranged as a detection area within an area where there are no feeder branches (for example, each feeder after branching in Figures 1 and 8). In estimating the ground fault location within a single feeder 12 (power transmission line) without branches, after detecting a ground fault based on the zero-phase sequence current, the process of identifying the fault feeder 12F (S120) described in the first and second embodiments is not required, and a specific power supply device 14 can be instructed to output a measurement current in response to the detection of a ground fault.

[0098] Furthermore, in estimating the location of a ground fault within a single feeder 12 (power transmission line), it is possible to estimate the location of the ground fault based on the estimated distance (the length of the distribution line) from a predetermined reference point based on the resonant frequency, without requiring specific information about the fault feeder 12F. In contrast, in a distribution system 1 having multiple branched feeders 12, there is a possibility that each feeder 12 has a point at the same distance from the reference point, so it is necessary to estimate the location of the ground fault by combining specific information about the fault feeder 12F.

[0099] The embodiments disclosed herein should be considered to be illustrative in all respects and not restrictive. The scope of the present disclosure is defined by the claims, not the above description, and is intended to include all modifications within the meaning and scope of the claims.

[0100] 1 Distribution system, 2A, 2B Fault location estimation device, 11 Distribution substation, 12 Feeder, 12F Fault feeder, 12H1, 12H, 12H2 Healthy feeder, 13 Switch, 14, 14A, 14B Power supply device, 15, 15a, 15c, 15d, 15e Current meter, 16 Earth fault fault point, 17 Earth capacitance, 17a, 17c, 17d Earth capacitance, 21 Current measurement result collection unit, 22 Zero-phase current detection unit, 23 Fault occurrence detection unit, 24 Data storage unit, 25 Fault occurrence point estimation unit, 40 Computer system, 50 Characteristic line, 101, 102 Resonant current waveform, 251 Frequency calculation unit, 252 Earth fault point matching unit, DRfp Data (estimation result), Dfdx Identification data, Dsl Selection data, Dx Distance, GND: ground, Id, Ida to Ide: current measurement data, Ipz: zero-phase current, Szc, Szca, Szcb: output command, frs: resonance frequency.

Claims

1. A ground fault location estimation device for a power distribution system provided with a transmission line on which at least one current measuring device is installed and a power supply device that outputs a current for measuring zero-phase current to the transmission line, comprising: a current measurement result collection unit that collects current measurement results notified from the current measuring device; a zero-phase current detection unit that detects the zero-phase current of the transmission line from the current measurement results; a ground fault occurrence detection unit that, when it detects the occurrence of a ground fault in the power distribution system based on the detected zero-phase current, instructs the power supply device to output the current; and a ground fault occurrence location estimation unit that estimates the occurrence location of the ground fault based on the zero-phase current detected by the current measurement result collection unit and the zero-phase current detection unit in response to the output of the current by the power supply device, wherein the ground fault occurrence location estimation unit calculates a resonance frequency from the waveform of the zero-phase current, and estimates the location of the occurrence location based on the calculated resonance frequency.

2. The ground fault location estimation device according to claim 1, wherein the ground fault occurrence detection unit estimates the location of the occurrence point according to an estimated distance from a predetermined reference point based on the resonant frequency to the occurrence point.

3. The power distribution system is provided with a plurality of branched transmission lines, and when the occurrence of a ground fault is detected, the ground fault occurrence detection unit further determines which of the plurality of transmission lines includes the occurrence point based on each of the zero-phase currents detected corresponding to each of the current measuring devices, and the ground fault occurrence point estimation unit estimates the position of the occurrence point according to information indicating the fault transmission line among the plurality of transmission lines that includes the occurrence point and an estimated distance from the power supply device to the occurrence point based on the resonant frequency.

4. A ground fault location estimation device as described in claim 1, wherein a plurality of the power supply devices are arranged at different locations in the power distribution system, a plurality of the current measuring devices are arranged on the power transmission line, and when the ground fault occurrence detection unit detects the occurrence of a ground fault, it further determines which of a plurality of sections divided by the arrangement positions of the plurality of current measuring devices includes the occurrence point based on the polarity of each of the zero-phase currents detected corresponding to each of the current measuring devices, and instructs one of the plurality of power supply devices selected according to the position of the fault section including the occurrence point on the plurality of power transmission lines to output the current.

5. A ground fault location estimation device as described in claim 4, wherein the power distribution system is provided with a plurality of branched transmission lines, each of which is provided with a plurality of current measuring devices, and when detecting a ground fault, the ground fault occurrence detection unit further determines which of the plurality of transmission lines includes the occurrence point based on the polarity of each of the zero-phase currents detected corresponding to each of the current measuring devices, and the ground fault occurrence point estimation unit estimates the location of the occurrence point based on information indicating the fault transmission line among the plurality of transmission lines that includes the occurrence point and an estimated distance from the power supply device to the occurrence point based on the resonant frequency.

6. A ground fault location estimation device according to any one of claims 1 to 5, wherein the power supply device is installed in a distribution substation of the power distribution system.

7. A method for estimating the location of a ground fault in a power distribution system provided with a transmission line on which at least one current meter is installed and a power supply device that outputs a current for measuring a zero-phase current to the transmission line, comprising the steps of: determining whether a ground fault has occurred in the power distribution system based on the zero-phase current of the transmission line detected from the current measurement results notified by the current meter; instructing the power supply device to output the current when the occurrence of the ground fault is detected; and estimating the location of the ground fault based on the zero-phase current detected from the current measurement results notified by the current meter after the power supply device outputs the current, wherein the estimating step calculates a resonant frequency from the waveform of the zero-phase current and estimates the location of the occurrence based on the calculated resonant frequency.

8. A method for estimating a ground fault location according to claim 7, wherein the estimating step estimates the location of the occurrence point according to an estimated distance from a predetermined reference point based on the resonant frequency to the occurrence point.

9. A method for estimating a ground fault location as described in claim 7, wherein the power distribution system is provided with a plurality of branched transmission lines, and the determining step, when the occurrence of a ground fault is detected, further determines which of the plurality of transmission lines includes the occurrence point based on each of the zero-phase currents detected corresponding to each of the current measuring devices, and the estimating step estimates the location of the occurrence point according to information indicating the fault transmission line among the plurality of transmission lines that includes the occurrence point and an estimated distance from the power supply device to the occurrence point based on the resonant frequency.

10. A method for estimating the location of a ground fault as described in claim 7, wherein the power distribution system is provided with a plurality of power supply devices at different locations, the transmission line is provided with a plurality of current measuring devices, and the determining step, when the occurrence of a ground fault is detected, further determines, based on the polarity of each of the zero-phase currents detected corresponding to each of the current measuring devices, which of a plurality of sections divided by the locations of the plurality of current measuring devices includes the occurrence point, and the instructing step instructs one of the plurality of power supply devices selected according to the location of the fault section including the occurrence point among the plurality of transmission lines to output the current.

11. A method for estimating a ground fault location as described in claim 10, wherein the power distribution system is provided with a plurality of branched transmission lines, each of which is provided with a plurality of current measuring devices, and the determining step, when the ground fault is detected, further determines which of the plurality of transmission lines includes the occurrence point based on the polarity of each of the zero-phase currents detected corresponding to each of the current measuring devices, and the estimating step estimates the location of the occurrence point according to information indicating the fault transmission line among the plurality of transmission lines that includes the occurrence point and an estimated distance from the power supply device to the occurrence point based on the resonant frequency.

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