Power-grid management device and power-grid management system

Abstract

Provided is a power-grid management device (300) for managing a power transmission / distribution grid (100) that includes a plurality of line-voltage meters (15a-15e). The plurality of line voltage meters (15a-15e) are provided respectively in a plurality of positions along a power transmission / distribution line (12). The power-grid management device (300) comprises: a clock-time acquisition unit (31) that acquires the time of occurrence when a ground fault has occurred in the power transmission / distribution line (12); a phase-change computing unit (32) that computes the amount of change in phase of the line voltages measured by each of the line-voltage meters (15a-15e) before and after the time of occurrence; and a position determining unit (33) that determines the position of the ground-fault occurrence on the basis of the amount of change in phase of the line voltages.

Description

Power system management device and power system management system

[0001] The present disclosure relates to a power system management device and a power system management system.

[0002] An electric power system is an operational system for supplying power to consumers' power receiving facilities, and is responsible for generating, transforming, transmitting, and distributing electricity. If an accident occurs in the electric power system, 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. One example of an accident that can occur in an electric power system is a ground fault. Conventionally, zero-phase sequence current and zero-phase sequence voltage have been monitored, and their phase relationship has been used to determine whether the fault point of a ground fault is on the power source side or the load side.

[0003] Japanese Patent No. 3221000 (Patent Document 1) discloses a method for detecting a ground fault based on the zero-phase sequence current flowing through a distribution line, and for determining the section of the distribution line where the ground fault occurs when the ground fault is detected. In this method, harmonic components of each phase current of the distribution line are detected, and positive and negative sequence components of the harmonic current are calculated based on these detected values. The direction of the ground fault location is determined by detecting changes over time in the positive and negative sequence components.

[0004] Patent No. 3221000

[0005] When determining the direction of a fault location by measuring each phase current and zero-phase current in a distribution line as in Patent Document 1, in order to improve the accuracy of determining the fault location, it is necessary to narrow the intervals between current measurement points according to the required accuracy, which requires increasing the number of current measurement points in the distribution line, resulting in the problem of incurring installation costs for new current measuring devices.

[0006] An object in one aspect of the present disclosure is to provide a power system management device that can accurately determine the location of a ground fault without providing a new current measuring device.

[0007] According to one embodiment, there is provided a power system management device for managing a power transmission and distribution system including a plurality of line voltage measuring devices. The plurality of line voltage measuring devices are respectively provided at a plurality of positions on the power transmission and distribution line. The power system management device includes a time acquisition unit that acquires the occurrence time of a ground fault that occurred on the power transmission and distribution line, a phase change calculation unit that calculates the phase change amount of the line voltages measured by each line voltage measuring device before and after the occurrence time, and a position determination unit that determines the occurrence position of the ground fault based on the phase change amount of each line voltage.

[0008] A power system management system according to another embodiment includes a power transmission / distribution system including a power transmission / distribution line and a plurality of line voltage measuring devices respectively provided at a plurality of positions on the power transmission / distribution line, a detection device for detecting a ground fault in the power transmission / distribution line, and a power system management device for managing the power transmission / distribution system. The power system management device includes a time acquisition unit that acquires the occurrence time of a ground fault that occurred in the power transmission / distribution line, a phase change calculation unit that calculates the phase change amount of the line voltages measured by each line voltage measuring device before and after the occurrence time, and a position determination unit that determines the occurrence position of the ground fault based on the phase change amount of each line voltage.

[0009] According to the present disclosure, the location of a ground fault can be determined with high accuracy without providing a new current measuring instrument.

[0010] FIG. 1 is a schematic diagram showing a configuration of a power system management system according to a first embodiment. FIG. 2 is a diagram showing an example of a functional configuration of a phase change calculation unit according to the first embodiment. FIG. 3 is a diagram showing an example of a calculation method for a zero crossing time. FIG. 4 is a diagram for explaining an example of a calculation method for an amount of phase change. FIG. 5 is a diagram showing an example of a functional configuration of a position determination unit according to the first embodiment. FIG. 6 is a diagram showing an example of a correlation between a distance and an amount of phase change according to the first embodiment. FIG. 7 is a diagram showing another example of a correlation between a distance and an amount of phase change according to the first embodiment. FIG. 8 is a diagram showing yet another example of a correlation between a distance and an amount of phase change according to the first embodiment.

[0011] Hereinafter, the present embodiment will be described with reference to the drawings. In the following description, the same components are denoted by the same reference numerals. The names and functions of these components are also the same. Therefore, detailed description thereof will not be repeated.

[0012] First Embodiment <System Configuration> Fig. 1 is a schematic diagram showing the configuration of a power system management system according to a first embodiment. Referring to Fig. 1, a power system management system 1000 includes a power distribution system 100, an external device 200, and a power system management device 300. The external device 200 and the power system management device 300 are configured to be able to communicate with each other. The external device 200 mainly functions as a detection device that detects a ground fault.

[0013] The power distribution system 100 includes a distribution substation 11 and a plurality of feeders 12 and 13. In this embodiment, the plurality of feeders 12 and 13 are three-phase power distribution lines, but the number of phases is not limited to this. In addition, the configuration of the power distribution lines of the power distribution system 100 is also an example and is not limited to this.

[0014] Feeder 12 is a fault feeder where a ground fault has occurred, and feeder 13 is a healthy feeder where no ground fault has occurred. Note that feeder 13 represents a collection of healthy feeders other than feeder 12 where a fault has occurred. In addition, in this embodiment, the grounding method of distribution system 100 is assumed to be an ungrounded method or a high-impedance grounded method, but is not limited to this.

[0015] The feeder 12 is provided with a zero-phase-sequence current meter 14 and line voltage meters 15a, 15b, 15c, 15d, and 15e (hereinafter collectively referred to as "line voltage meters 15"). A fault point 16 indicates the location where a ground fault occurs. FIG. 1 shows an example in which the fault point 16 is located between the line voltage meters 15c and 15d. The zero-phase-sequence current meter 14 measures the zero-phase-sequence current at the installation location. The line voltage meter 15 measures the line voltage at the corresponding installation location. The line voltage meter 15 measures the voltage between each phase of the three U-phase, V-phase, and W-phase lines (for example, between the U phase and the V phase, between the V phase and the W phase, and between the W phase and the U phase). The installation locations of the multiple line voltage meters 15a to 15e are merely examples and are not limited to these.

[0016] The multiple line voltage meters 15a to 15e are provided at multiple positions on the feeder 12. The line voltage meter 15 may be configured to measure the line voltage from the low-voltage side via a transformer such as a pole transformer. The line voltage measured by the line voltage meter 15 may also be a value measured by a voltage sensor mounted on a smart meter, power conditioner, or the like of consumer-side equipment. To mitigate the effects of measurement errors, information about the line voltage measured by multiple meters below the pole transformer, such as voltage phase fluctuations, may be averaged and treated as a single piece of data, which may be used to determine (locate) the location of a ground fault.

[0017] The zero-phase-sequence current meter 14 is provided on the feeder 12 closest to the power source (i.e., on the distribution substation 11 side), but may be provided at another location on the feeder 12. Furthermore, since a zero-phase-sequence current is also generated in the feeder 13 when a ground fault occurs in the feeder 12, the zero-phase-sequence current meter 14 may be provided on the feeder 13. The role of the zero-phase-sequence current meter 14 is to detect the time when the ground fault occurs. Therefore, the time when the ground fault occurs may be detected using the zero-phase-sequence voltage measured by a zero-phase-sequence voltage meter instead of the zero-phase-sequence current meter 14.

[0018] The feeder 13 is provided with an earth capacitance 17. The earth capacitance 17 represents the aggregate of earth capacitances distributed due to the distribution lines, customer equipment, cables, etc. in the feeder 13. The earth capacitance 17 affects the magnitude of the fault current when a ground fault occurs.

[0019] The external device 200 mainly includes a fault detection unit 21 and a position storage unit 22. The fault detection unit 21 receives an input of a zero-phase-sequence current measurement value measured by the zero-phase-sequence current meter 14. The fault detection unit 21 detects the occurrence of a ground fault based on the zero-phase-sequence current measurement value and calculates the time of occurrence. The fault detection unit 21 outputs (e.g., transmits) the time of occurrence of the ground fault to the power system management device 300.

[0020] For example, the fault detection unit 21 calculates the effective value of the zero-phase current, and calculates the time when the effective value exceeds a threshold as the occurrence time of a ground fault that occurred in the feeder 12. However, the method for calculating the occurrence time of a ground fault is not limited to this, and the fault detection unit 21 may be configured to detect an increase in the zero-phase current due to the occurrence of a ground fault, and calculate the time when the increase occurred.

[0021] The fault detection unit 21 may use any of the instantaneous value, effective value, and amplitude of the zero-phase current to detect the occurrence of a ground fault. When the fault detection unit 21 detects a ground fault in which the zero-phase current contains many harmonics or a minute ground fault in which the zero-phase current is small compared to a complete ground fault, a threshold value for detecting such occurrence is appropriately set. Furthermore, the fault detection unit 21 may calculate the occurrence time of a ground fault based on the measured value of the zero-phase voltage instead of the zero-phase current. Specifically, the fault detection unit 21 detects an increase in the zero-phase voltage based on the measured value of the zero-phase voltage and calculates the occurrence time of a ground fault.

[0022] The position storage unit 22 stores installation position information indicating the location where each of the plurality of line voltage measuring devices 15a, 15b, 15c, 15d, and 15e is installed. The installation position information includes information indicating the distance from a reference position on the power source side of the power distribution system 100 (for example, the location where the power distribution substation 11 is installed) to the location where each of the plurality of line voltage measuring devices 15a to 15e is installed. The installation position information is output to the power system management device 300.

[0023] The fault detection unit 21 and the position storage unit 22 may be implemented in separate devices, or may be included in the power system management device 300 .

[0024] The power system management device 300 is a device for managing the power distribution system 100. Specifically, the power system management device 300 includes, as main functional components, a time acquisition unit 31, a phase change calculation unit 32, and a position determination unit 33. The time acquisition unit 31 acquires the occurrence time of a ground fault calculated by the fault detection unit 21. The occurrence time is output to the phase change calculation unit 32.

[0025] The phase change calculation unit 32 calculates the phase fluctuation (i.e., the amount of phase change) in the line voltages measured by each of the line voltage measuring devices 15a to 15e before and after the occurrence of the ground fault (i.e., before and after the time of the occurrence of the ground fault) using the occurrence time of the ground fault input from the time acquisition unit 31. The specific configuration of the phase change calculation unit 32 will be described later.

[0026] The position determination unit 33 determines the location of the ground fault based on the distance from the distribution substation 11 to the location where the line voltage measuring instrument 15 is installed and the amount of phase change of each line voltage calculated by the phase change calculation unit 32, and outputs the location of the occurrence. The specific configuration of the position determination unit 33 will be described later.

[0027] The hardware of the external device 200 and the power system management device 300 is typically configured mainly with a microcomputer. In this case, each of the external device 200 and the power system management device 300 includes a processor, a main memory device, a secondary memory device, a communication interface, a display, an input device, etc.

[0028] The processor is typically composed of a CPU (Central Processing Unit) or an MPU (Multi Processing Unit). The main storage device is typically a volatile storage medium such as a DRAM (Dynamic Random Access Memory) and stores the codes of various programs, including the OS, executed by the processor, as well as various work data required to execute the various programs. The secondary storage device is a non-volatile storage medium such as a hard disk or an SSD (Solid State Drive) and stores various programs, including the OS, as well as various setting values.

[0029] The communication interface mediates data transmission between the processor and an external device. Communication via the communication interface is performed using a wired network, a wireless network, or a combination of these. The display is, for example, a liquid crystal display, an organic electroluminescence (EL) display, or the like. The input device is, for example, a keyboard, buttons, a mouse, a touch panel, or the like.

[0030] Each function of the external device 200 and the power system management device 300 described above may be realized by, for example, a processor that executes a program stored in an internal memory (for example, a main storage device, a secondary storage device, etc.). Also, at least a part of each function may be configured using circuits such as an FPGA (Field Programmable Gate Array) and an ASIC (Application Specific Integrated Circuit).

[0031] <Configuration of Phase Change Calculation Unit> Fig. 2 is a diagram showing an example of the functional configuration of a phase change calculation unit according to embodiment 1. Referring to Fig. 2, phase change calculation unit 32 includes a data extraction unit 321, a filter unit 322, a zero-cross time calculation unit 323, and a change amount calculation unit 324.

[0032] The data extraction unit 321 extracts measurement data around the time when a ground fault occurs from the measurement data of the line voltage measured by the line voltage meter 15. The length of the data extracted by the data extraction unit 321 is, for example, a data length equivalent to approximately 0.5 to 1.0 seconds around the time of the occurrence. However, the length of the extracted data may be set appropriately taking into consideration the time required for calculation processing, the capacity of the internal memory, etc.

[0033] The data extraction unit 321 may specify a time range for the line voltage meter 15 and receive measurement data extracted according to the specified time range from the line voltage meter 15. In this case, the data extraction unit 321 notifies the line voltage meter 15 of the occurrence time of the ground fault acquired from the time acquisition unit 31. The line voltage meter 15 transmits measurement data around the occurrence time of the ground fault to the data extraction unit 321.

[0034] The filter unit 322 performs filtering to remove noise and the like superimposed on the measurement data extracted by the data extraction unit 321. The filter unit 322 performs filtering using, for example, an FIR (finite impulse response) filter.

[0035] The zero-cross time calculation unit 323 calculates the time when the waveform of the measurement data filtered by the filter unit 322 crosses zero.

[0036] 3 is a diagram showing an example of a method for calculating the zero-cross time. Referring to Fig. 3, the zero-cross time calculation unit 323 calculates the zero-cross time as the time at which a straight line, which is linearly approximated using values ​​immediately before and after a change in the positive or negative sign in the filtered measurement data, intersects with zero.

[0037] Referring again to Figure 2, the change amount calculation unit 324 calculates the amount of phase change in the line voltage before and after the occurrence of the ground fault based on the zero cross time calculated by the zero cross time calculation unit 323 and the time when the ground fault occurred.

[0038] FIG. 4 is a diagram illustrating an example of a method for calculating the amount of phase change. Referring to FIG. 4, the amount of phase change calculation unit 324 calculates the amount of phase change using the zero cross time t1 before the occurrence of a ground fault and the zero cross time t2 after the occurrence of the ground fault. The amount of phase change Pc is calculated, for example, by the following equation (1). The period T is the system voltage period of the power distribution system, and is, for example, 20 ms. R represents the remainder when "(t2-t1) / T" is calculated up to the integer part.

[0039] Pc = (R / T) × 360° (1) Note that T may be a period calculated using the zero-crossing time calculated by the zero-crossing time calculation unit 323. Furthermore, taking into account errors and the like, the amount of phase change may be calculated using an average value of the zero-crossing times of multiple periods before and after the occurrence of a ground fault. Furthermore, taking into account time synchronization discrepancies between multiple line voltage measuring instruments 15, a dead zone may be provided before and after the time tx at which the ground fault occurs, as shown in FIG. 4 .

[0040] The method for calculating the amount of phase change is not limited to the above method, and for example, the amount of phase change may be calculated by combining a zero-cross detection circuit and a counter circuit, which are analog circuits.

[0041] 5 is a diagram showing an example of the functional configuration of position determination unit 33 according to embodiment 1. Referring to Fig. 5, position determination unit 33 includes a distance acquisition unit 331, a function approximation unit 332, a change point calculation unit 333, and an exception processing unit 334.

[0042] The distance acquisition unit 331 acquires (e.g., receives) information indicating the distance from the distribution substation 11 to the location where each of the multiple line voltage measuring instruments 15a to 15e is installed from the external device 200 (specifically, the position memory unit 22).

[0043] The function approximation unit 332 performs function approximation based on the correlation between the distance D from the distribution substation 11 to the installation location of the line voltage meter 15, acquired by the distance acquisition unit 331, and the phase change Pc of the line voltage measured by the line voltage meter 15.

[0044] FIG. 6 is a diagram illustrating an example of the correlation between distance and phase change amount according to the first embodiment. The horizontal axis of FIG. 6 represents distance D, and the vertical axis represents phase change amount Pc. The phase change amount Pc represents the phase change amount Pc of the line voltage between one of the phases (e.g., U-phase-V phase, V-phase-W phase, W-phase-U phase) (e.g., U-phase-V phase). Distances Da to De represent the distances between distribution substation 11 and line voltage measuring instruments 15a to 15e, respectively. Each point in FIG. 6 represents a plot of the phase change amount Pc corresponding to distances Da to De. Here, it is assumed that fault point 16 is located between line voltage measuring instrument 15c and line voltage measuring instrument 15d, as shown in FIG. 1.

[0045] The function approximation unit 332 approximates a plurality of plot points showing the correlation between the distance D and the phase change amount Pc with a linear function (i.e., linear approximation) using the least squares method. In the example of Fig. 6, the function approximation unit 332 divides the section between the position of the distribution substation 11 (i.e., the reference position) and the position of the line voltage meter 15e that is farthest from the reference position into two sections. For example, the section is divided into a section X1 where the distance D is equal to or less than the distance Dc, and a section X2 where the distance D is greater than the distance Dc.

[0046] Next, the function approximation unit 332 derives an approximate line 61 based on the multiple plot points in the section X1 (i.e., the plot points corresponding to the distances Da to Dc), and derives an approximate line 62 based on the multiple plot points in the section X2 (i.e., the plot points corresponding to the distances Dd and De). The function approximation unit 332 is configured to set the sections X1 and X2 so as to minimize the error between the approximate line and the multiple plot points, and to derive approximate lines corresponding to each of the sections X1 and X2. In this way, an appropriate approximate line is derived.

[0047] The change point calculation unit 333 determines whether there is a change point where the absolute value of the rate of change of the phase change Pc with respect to the distance D changes from a state where it is greater than the threshold value Th to a state where it is equal to or less than the threshold value Th, based on the correlation between the distance D and the phase change Pc. If there is such a change point, the change point calculation unit 333 determines that the position indicating the distance corresponding to the change point (for example, the distance Dx in FIG. 6 ) is the position where the ground fault occurred.

[0048] The reason why a change point is determined to be the location of a ground fault will be explained. First, when a ground fault occurs, a ground fault current flows, causing an impedance voltage drop in the distribution line. This causes a phase fluctuation in the line-to-line voltage. Furthermore, when a ground fault occurs, the ground fault current flows from the distribution system toward the fault point, so the direction of the ground fault current differs between a point on the power source side of the fault point (e.g., the distribution substation side) and a point on the terminal side (e.g., the opposite side from the distribution substation). Therefore, since the voltage phase fluctuation appears different between the power source side and the terminal side of the fault point, the change point in the voltage phase fluctuation can be identified as the location of the ground fault.

[0049] In the example of FIG. 6 , approximate lines 61 and 62 are derived by the function approximation unit 332. The slope of approximate line 61 is much smaller than the slope of approximate line 62. That is, the slope of approximate line 61 is greater than threshold value Th, and the slope of approximate line 62 is smaller than threshold value Th. Therefore, in the example of FIG. 6 , the change point calculation unit 333 determines that there is a change point Y where the absolute value of the rate of change changes from a state greater than threshold value Th to a state equal to or less than threshold value Th. Specifically, the change point calculation unit 333 calculates the intersection of approximate line 61 and approximate line 62, and determines this intersection as change point Y.

[0050] Although the above description has been given of a configuration in which the function approximation unit 332 derives the two approximate lines 61 and 62, the configuration is not limited to this. The function approximation unit 332 may derive the approximate curve by curve approximation (for example, approximation with a quadratic function) using multiple plot points at distances Da to De. In this case, the slope of the tangent to the approximate curve corresponds to the absolute value of the rate of change of the phase change amount Pc with respect to the distance D. Therefore, when the change point calculation unit 333 determines that the slope of the tangent has changed from a state in which it is greater than the threshold value Th to a state in which it is equal to or less than the threshold value Th, it calculates the point at which the change occurred as the change point Y.

[0051] The function approximation unit 332 may be configured to calculate multiple straight lines by connecting two adjacent plot points with a straight line. In this case, the change point calculation unit 333 calculates the point where the slope of the straight line changes from being greater than the threshold value Th to being smaller than the threshold value Th as the change point Y.

[0052] Referring again to FIG. 5, when the change point calculation unit 333 determines that the change point Y does not exist, the exception processing unit 334 executes a process for determining the location where a ground fault has occurred.

[0053] FIG. 7 is a diagram illustrating another example of the correlation between distance and phase change amount according to the first embodiment. FIG. 7 illustrates an example in which the fault point 16 is located between the distribution substation 11 and the line voltage measuring instrument 15a. In this case, it can be seen that the phase change amount Pc hardly changes with respect to the distance D. The function approximation unit 332 linearly approximates multiple plot points that indicate the correlation between the distance D and the phase change amount Pc. In the example of FIG. 7 , the function approximation unit 332 determines that the error between each plot point and an approximated line 63 derived based on five plot points is less than a specified value. Therefore, the function approximation unit 332 derives an approximated line 63 corresponding to a single section from the distribution substation 11 to the line voltage measuring instrument 15a, without setting two sections as in the example of FIG. 6 .

[0054] The slope of the approximation line 63 is equal to or smaller than the threshold value Th. Therefore, in the example of Fig. 7, the change-point calculation unit 333 determines that there is no change point Y at which the absolute value of the rate of change of the phase change amount Pc with respect to the distance D changes from a state in which it is greater than the threshold value Th to a state in which it is equal to or smaller than the threshold value Th.

[0055] Upon receiving the determination result, the exception processing unit 334 evaluates the relationship between the absolute value of the rate of change of the phase change amount Pc with respect to the distance D and the threshold value Th. In the example of Fig. 7, the exception processing unit 334 determines that the absolute value of the rate of change is not greater than the threshold value Th. In this case, the exception processing unit 334 determines that a ground fault has occurred between the position of the line voltage meter 15a closest to the distribution substation 11 and the position of the distribution substation 11 (i.e., on the power supply side of the line voltage meter 15a).

[0056] In this way, when the fault point 16 is located between the distribution substation 11 and the line voltage measuring instrument 15a, the phase change amount Pc hardly changes with the distance D because the earth fault current is smaller at the end side of the fault point 16.

[0057] 8 is a diagram showing yet another example of the correlation between distance and phase change amount according to the first embodiment. In this example, fault point 16 is located closer to the distal end than line voltage measuring instrument 15e. In this case, it can be seen that phase change amount Pc changes in proportion to distance D.

[0058] The function approximation unit 332 linearly approximates the multiple plot points that indicate the correlation between the distance D and the phase change amount Pc. In the example of FIG. 8 , the function approximation unit 332 determines that the error between each plot point and an approximated line 64 derived based on five plot points is less than a specified value. Therefore, the function approximation unit 332 derives an approximated line 64 that corresponds to one section from the distribution substation 11 to the line voltage meter 15e. The slope of the approximated line 64 is greater than the threshold value Th.

[0059] In the example of FIG. 8, the change point calculation unit 333 determines that the change point Y does not exist because the phase change amount Pc changes in almost proportion to the distance D.

[0060] Upon receiving the determination result, the exception processing unit 334 evaluates the relationship between the absolute value of the rate of change of the phase change amount Pc with respect to the distance D and the threshold value Th. In the example of Fig. 8, the exception processing unit 334 determines that the absolute value of the rate of change remains greater than the threshold value Th. In this case, the exception processing unit 334 determines that a ground fault has occurred at a position farther away from the position of the line voltage measuring instrument 15e, which is farthest from the distribution substation 11.

[0061] The reason why the phase change amount Pc changes approximately proportionally to the distance D when the fault point 16 is located closer to the terminal than the line voltage measuring device 15e is as follows. Specifically, a ground fault current flows toward the fault point 16 at a point closer to the power source than the fault point 16. If the magnitude of the ground fault current flowing through each of the multiple line voltage measuring devices 15 is constant, the magnitude of the phase fluctuation of the line voltage at each of the multiple line voltage measuring devices 15 is approximately proportional to the impedance from the distribution substation 11 to the installation position of that line voltage measuring device 15. The impedance from the distribution substation 11 to that installation position is also approximately proportional to the distance from the distribution substation 11 to that installation position. Therefore, the phase change amount Pc increases as the distance D increases.

[0062] <Processing Procedure> Fig. 9 is a flowchart showing an example of a processing procedure in the power system management system according to the first embodiment. Referring to Fig. 9, fault detection unit 21 of external device 200 determines whether or not a ground fault has occurred based on the measurement value of the zero-phase-sequence current measured by zero-phase-sequence current meter 14 (step S10). If a ground fault has not occurred (NO in step S10), the processing of step S10 is repeated.

[0063] If a ground fault has occurred (YES in step S10), the fault detection unit 21 calculates the time of occurrence of the ground fault based on the measured value of the zero-phase current (step S12). Subsequently, the time acquisition unit 31 of the power system management device 300 acquires the time of occurrence of the ground fault from the fault detection unit 21 (step S14).

[0064] The phase change calculation unit 32 of the power system management device 300 acquires the measurement data of the time when the ground fault occurred and the line voltages measured by the plurality of line voltage measuring instruments 15 (step S16). The phase change calculation unit 32 extracts measurement data around the time when the ground fault occurred from the measurement data of the line voltages measured by the plurality of line voltage measuring instruments 15 (step S18). The phase change calculation unit 32 performs filtering to remove noise and the like superimposed on the extracted measurement data (step S20).

[0065] The phase change calculation unit 32 calculates the zero-crossing time when the waveform of the filtered measurement data crosses zero (step S22).The phase change calculation unit 32 calculates the amount of phase change in the line voltage before and after the ground fault occurs based on the zero-crossing time and the time when the ground fault occurs (step S24).

[0066] The position determination unit 33 of the power system management device 300 obtains the amount of phase change before and after the occurrence of a ground fault for each of the multiple line voltage meters 15 from the phase change calculation unit 32 (step S26). The position determination unit 33 obtains installation position information for the line voltage meters 15 from the external device 200 (step S28). Specifically, the position determination unit 33 obtains the distance (e.g., distances Da to De) from the distribution substation 11 to the installation position of each of the multiple line voltage meters 15.

[0067] The position determination unit 33 performs function approximation (step S30) based on the correlation between the distance D from the distribution substation 11 to the installation position of the line voltage meter 15 and the phase change Pc of the line voltage measured by the line voltage meter 15. The position determination unit 33 determines whether or not there is a change point Y at which the absolute value of the rate of change of the phase change Pc with respect to the distance D changes from a state in which it is greater than a threshold Th to a state in which it is equal to or less than the threshold Th (step S32).

[0068] If a change point Y exists (YES in step S32), the position determination unit 33 determines that the position indicating the distance corresponding to the change point Y (for example, the distance Dx in Figure 6) is the position where a ground fault occurred (step S34), and terminates the processing.

[0069] If change point Y does not exist (NO in step S32), the position determination unit 33 determines the location of the ground fault in accordance with the exception condition (step S36) and terminates the process. Specifically, if the exception condition is met that the absolute value of the rate of change does not become greater than threshold value Th, the position determination unit 33 determines that the ground fault has occurred on the power supply side of line voltage meter 15a. On the other hand, if the exception condition is met that the absolute value of the rate of change remains greater than threshold value Th, the position determination unit 33 determines that the ground fault has occurred on the distal side of line voltage meter 15e.

[0070] <Advantages> According to the first embodiment, the location of a ground fault can be determined using the line voltage measured by a line voltage meter installed in a feeder. The line voltage can also be measured from the low-voltage side of the power distribution system, and can also be measured using existing consumer-side equipment (e.g., a smart meter, a power conditioner, etc.). Therefore, there is no need to install a new meter, and the location of a ground fault can be accurately determined while reducing the installation costs of the meter.

[0071] Embodiment 2 Fig. 10 is a schematic diagram showing the configuration of a power system management system according to embodiment 2. Referring to Fig. 10, a power system management system 1000A includes a power distribution system 100A, an external device 200A, and a power system management device 300A.

[0072] 1 in that a branch line 18 is provided that branches off from the trunk line of the feeder 12. A plurality of line voltage meters 15f to 15h are provided at a plurality of positions on the branch line 18. FIG. 10 shows an example in which the fault point 16 is located between the line voltage meters 15f and 15g on the branch line 18.

[0073] The configuration of external device 200A corresponds to a configuration in which position storage unit 22 of external device 200 in Fig. 1 is replaced with position storage unit 22A. Position storage unit 22A stores installation position information indicating the positions where line voltage measuring devices 15a to 15h are installed.

[0074] The configuration of the power system management device 300A corresponds to a configuration in which the phase change calculation unit 32 and the position determination unit 33 of the power system management device 300 in Fig. 1 are replaced with a phase change calculation unit 32A and a position determination unit 33A, respectively. The phase change calculation unit 32A calculates the phase change amount Pc of the line voltages measured by the line voltage meters 15a to 15h before and after the time when the ground fault occurs. The method of calculating the phase change amount Pc is the same as that described above.

[0075] Fig. 11 is a diagram showing an example of a functional configuration of position determination unit 33A according to Embodiment 2. Referring to Fig. 11, position determination unit 33A includes a distance acquisition unit 331A, a function approximation unit 332A, a change point calculation unit 333A, an exception processing unit 334A, and a branch line determination unit 335A.

[0076] The distance acquisition unit 331A acquires, from the external device 200A, information indicating the distance from the distribution substation 11 to the positions where each of the line voltage measuring devices 15a to 15h is installed. The function approximation unit 332A performs function approximation based on the correlation between the distance D from the distribution substation 11 to the installation position of the line voltage measuring device 15 (e.g., line voltage measuring devices 15a to 15e) installed on the trunk line of the feeder 12 and the phase change Pc of the line voltage measured by the line voltage measuring device 15.

[0077] FIG. 12 is a diagram showing an example of the correlation between distance and phase change amount according to the second embodiment. The definitions of the horizontal and vertical axes, distances Da to De and Dx, and change point Y in FIG. 12 are the same as those described in FIG. 6. Function approximation unit 332A derives approximate line 71 based on multiple plot points in section X1, and derives approximate line 72 based on multiple plot points in section X2, using the same method as above. Change point calculation unit 333A determines that change point Y exists using the same method as above.

[0078] 11 again, in the example of Fig. 12, since there is a change point Y, the exception processing unit 334 does not perform the process of determining the occurrence position of a ground fault. Next, the branch line determination unit 335A determines whether or not there is a branch line 18 near the change point Y. For example, the branch line determination unit 335A determines whether or not there is a branch line 18 within a specified distance from the position indicated by the distance Dx corresponding to the change point Y. Note that position information of the branch line 18 is stored in advance in the internal memory of the power system management device 300A.

[0079] Here, the branch line determination unit 335A determines that a branch line 18 exists near the change point Y. In this case, the branch line determination unit 335A extracts one or more line voltage meters 15 (for example, line voltage meters 15f to 15h) provided on the branch line 18.

[0080] The function approximation unit 332A extracts the line voltage measuring instrument 15c that is located on the trunk line of the feeder 12 and is provided at a position closest to the branch line 18. The function approximation unit 332A performs function approximation based on the correlation between the distance D from the distribution substation 11 to the installation position of the line voltage measuring instrument 15c, 15f to 15h and the phase change amount Pc of the line voltage measured by the line voltage measuring instrument 15c, 15f to 15h.

[0081] 13 is a diagram showing another example of the correlation between distance and the amount of phase change according to the second embodiment. Referring to FIG. 13, function approximation unit 332A performs function approximation in a similar manner. Specifically, function approximation unit 332A divides the section between the position of distribution substation 11 and the position of line voltage meter 15h that is farthest from the reference position into two sections. For example, the section is divided into section Xa1 where distance D is equal to or less than distance Df, and section Xa2 where distance D is greater than distance Df.

[0082] Next, the function approximation unit 332A derives an approximate straight line 73 based on multiple plot points in the section Xa1 (i.e., plot points corresponding to distances Dc and Df), and derives an approximate straight line 74 based on multiple plot points in the section Xa2 (i.e., plot points corresponding to distances Dg and Dh).

[0083] The change point calculation unit 333A calculates the change point Ya in the same manner as above, and determines that the position indicating the distance corresponding to the change point Ya (for example, the distance Dxa in FIG. 13 ) is the position where the ground fault has occurred. That is, the change point calculation unit 333A determines that the position where the ground fault has occurred is between the line voltage measurer 15f and the line voltage measurer 15g.

[0084] 10 has been described as a configuration in which a change point Y exists, but the same applies to a case in which a change point Y does not exist. For example, if branch line 18 is connected to the trunk line between distribution substation 11 and line voltage measuring instrument 15a and fault point 16 exists on branch line 18, change point calculation unit 333A determines that change point Y does not exist. In this case, the relationship between distance D and phase change amount Pc is the correlation shown in FIG. 7 , so exception processing unit 334A tentatively determines that a ground fault has occurred between line voltage measuring instrument 15a and distribution substation 11.

[0085] Next, branch line determination unit 335A determines that branch line 18 exists near the location where the provisionally determined ground fault has occurred, and extracts one or more line voltage meters 15 (for example, line voltage meters 15f to 15h) provided on branch line 18. The subsequent processing by function approximation unit 332A and change point calculation unit 333A is the same as the processing described above.

[0086] Furthermore, even when branch line 18 is connected to the trunk line closer to the end than line voltage meter 15e and fault point 16 exists on branch line 18, change point calculation unit 333A determines that change point Y does not exist. In this case, the correlation between distance D and phase change amount Pc is as shown in FIG. 8 , so exception processing unit 334A provisionally determines that a ground fault has occurred at a position farther away than the position of line voltage meter 15e.

[0087] Next, branch line determination unit 335A determines that branch line 18 exists near the location where the provisionally determined ground fault has occurred, and extracts one or more line voltage meters 15 provided on branch line 18. The subsequent processing by function approximation unit 332A and change point calculation unit 333A is the same as the processing described above.

[0088] As described above, the position determination unit 33A determines the location of the ground fault based on the phase change Pc of the line voltage measured by the line voltage meter 15c located closest to the branch line 18 and each of the line voltage meters 15f to 15h located on the branch line 18.

[0089] 14 is a flowchart showing an example of a processing procedure in the power system management system according to embodiment 2. Referring to FIG. 14, the processing from steps S10 to S32 is similar to the processing in FIG.

[0090] If change point Y exists (YES in step S32), position determination unit 33A executes the process of step S42. If change point Y does not exist (NO in step S32), position determination unit 33A provisionally determines the location of the ground fault (i.e., the ground fault point) in accordance with the exceptional condition (step S40). Specifically, position determination unit 33A provisionally determines that the ground fault point exists on the power supply side of line voltage meter 15a or on the distal end side of line voltage meter 15e.

[0091] Next, the position determination unit 33A determines whether or not a branch line 18 is present near the change point Y or the provisionally determined fault point (step S42). If the branch line 18 is not present (NO in step S42) and the change point Y is present (YES in step S32), the position determination unit 33A determines that the position indicating the distance corresponding to the change point Y is the location where a ground fault has occurred (step S46), and ends the processing. On the other hand, if the branch line 18 is not present (NO in step S42) and the fault point has been provisionally determined in accordance with the exception condition (step S40), the position determination unit 33A determines that the provisionally determined fault point is the location where a ground fault has occurred (step S46), and ends the processing.

[0092] On the other hand, if a branch line 18 is present (YES in step S42), the position determination unit 33A extracts one or more line voltage meters 15 provided on the branch line 18 (step S44). Next, the position determination unit 33A performs function approximation based on the correlation between the distance D and the phase change amount Pc of the line voltage measured by the line voltage meter 15 provided closest to the branch line 18 and each of the extracted one or more line voltage meters 15 (step S30). The position determination unit 33A performs the processes from step S32 onwards.

[0093] <Advantages> According to the second embodiment, even if a ground fault occurs on the branch line 18 branching off from the trunk line of the feeder 12, the location of the ground fault can be determined with high accuracy.

[0094] Embodiment 3 Fig. 15 is a schematic diagram showing the configuration of a power system management system according to embodiment 3. Referring to Fig. 15, a power system management system 1000B includes a power distribution system 100B, an external device 200B, and a power system management device 300B.

[0095] The power distribution system 100B differs from the power distribution system 100 in that a high-voltage single-phase power distribution line 40 is drawn from the trunk (i.e., three-phase power distribution line) of the feeder 12. The high-voltage single-phase power distribution line 40 drawn from the trunk of the feeder 12 is connected to a single-phase pole transformer 41 and stepped down to a low-voltage single-phase power distribution line 42. Voltmeters 43a, 43b, and 43c (hereinafter collectively referred to as "voltmeters 43") are installed on the low-voltage single-phase power distribution line 42 to measure the voltage of the low-voltage single-phase power distribution line 42. The voltage meter 43 may be a meter installed in consumer-side equipment such as a smart meter or a home power conditioner. Note that the configuration of the power distribution line of the power distribution system 100B and the installation locations of the line voltage meters 15a, 15b, 15d, and 15e and the voltmeters 43a to 43c are merely examples.

[0096] The configuration of external device 200B corresponds to a configuration in which position memory unit 22 of external device 200 in Fig. 1 is replaced with position memory unit 22B. Position memory unit 22B stores installation position information indicating the locations where line voltage meters 15a, 15b, 15d, and 15e and voltage meters 43a to 43c are installed.

[0097] The configuration of the power system management device 300B corresponds to a configuration in which the phase change calculation unit 32 and the position determination unit 33 of the power system management device 300 in Fig. 1 are replaced with a phase change calculation unit 32B and a position determination unit 33B, respectively, and a line-to-line determination unit 34B is further added. The phase change calculation unit 32B calculates the phase change Pc of the three line-to-line voltages measured by the line voltage meter 15 before and after the time when the ground fault occurred. The phase change calculation unit 32B also calculates the phase change Pc of the voltage measured by the voltage meter 43 before and after the time when the ground fault occurred.

[0098] The line determination unit 34B distinguishes between the line voltage Vuv between U and V, the line voltage Vvw between V and W, and the line voltage Vwu between W and U, based on the magnitude of the phase change Pc of the three line voltages measured by the line voltage meter 15. That is, the line determination unit 34B classifies the three measured line voltages into the line voltage Vuv, the line voltage Vvw, and the line voltage Vwu.

[0099] For example, the line-to-line determination unit 34B classifies the line voltage corresponding to the largest phase change among the phase changes of the three line voltages as the line voltage Vuv, the line voltage corresponding to the second largest phase change as the line voltage Vvw, and the line voltage corresponding to the third largest phase change as the line voltage Vwu. This makes it possible to appropriately determine which line voltage corresponds to which of the three line voltages measured by the line voltage meter 15, even if the line-to-line voltages corresponding to the three line voltages are not known (for example, if they are not known in advance by the system operator).

[0100] Furthermore, the line-to-line determination unit 34B determines between which two phases (e.g., U-phase-V phase, V-phase-W phase, W-phase-U phase) the voltage measured by the voltage meter 43 is measured. Consider, for example, voltage meter 43a. In this case, the line-to-line determination unit 34B extracts line voltage meters 15 located near voltage meter 43a (e.g., located within a specified distance from the installation position of voltage meter 43a). In this case, line voltage meters 15b and 15d are extracted.

[0101] The line-to-line determination unit 34B compares the phase change amounts of the three line voltages Vuv, Vvw, and Vwu measured by the line voltage meters 15b and 15d with the phase change amount of the voltage Va measured by the voltage meter 43a. Of the three line voltages Vuv, Vvw, and Vwu, the line-to-line determination unit 34B selects the line voltage having the phase change amount closest to the phase change amount of the voltage Va. For example, assume that the line voltage Vuv is selected. In this case, the line-to-line determination unit 34B determines that the voltage Va is measured between the two phases (i.e., between the U phase and the V phase) corresponding to the selected line voltage Vuv.

[0102] 16 is a flowchart showing an example of a processing procedure in the power system management system according to embodiment 3. Referring to FIG. 16, the processing from steps S10 to S24 is similar to the processing in FIG.

[0103] The line-to-line determination unit 34B identifies the line-to-line voltages Vuv, Vvw, and Vwu based on the magnitude of the phase change Pc of the three line voltages measured by the line voltage meter 15 (step S50). The line-to-line determination unit 34B also determines between which two of the phases the voltage measured by the voltage meter 43 is the voltage measured. The processing from step S26 onwards is the same as the processing in FIG. 9 .

[0104] <Advantages> According to the third embodiment, it is possible to determine between which two phases the measured line voltage was measured, so there is no need to know in advance between which two phases each of the three line voltages measured by the line voltage meter 15 was measured.

[0105] Other Embodiments. (1) In the above-described embodiment, as an example, a configuration has been described in which the power system management device 300 is a device for managing the power distribution system 100. However, the present invention is not limited to this configuration. For example, the power system management device 300 may be a device for managing a power transmission system. In this case, the distribution substation 11 may be a power transmission substation, and the feeders 12 and 13 may be three-phase transmission lines. That is, the power system management device 300 may be a device for managing a power transmission and distribution system. Furthermore, the feeders 12 and 13 may be transmission lines, such as transmission lines used to transmit power from a power plant to a substation or between substations, and distribution lines used to transmit power from a substation to a consumer.

[0106] (2) In the above-described embodiment, the phase change calculation unit 32 does not have to be implemented in the power system management apparatus 300. For example, the line voltage meter 15 may have the function of the phase change calculation unit 32. In this case, the occurrence time of the ground fault acquired by the time acquisition unit 31 is notified to the line voltage meter 15. In addition, the amount of phase change calculated by the line voltage meter 15 is input to the position determination unit 33 of the power system management apparatus 300.

[0107] (3) In the second embodiment described above, if the location of the ground fault occurring after the branch line 18 cannot be determined because, for example, the line voltage meter 15 is not installed on the branch line 18, the location determination unit 33A may determine that the location corresponding to the change point Y is the location of the ground fault. Alternatively, the location determination unit 33A may determine that the location of the ground fault exists on the branch line 18. The same applies to cases where the line voltage meter 15 is installed on the branch line 18 but it is not necessary to determine the location of the ground fault after the branch line 18 (for example, when the range of the distribution system after the branch line 18 is sufficiently narrow and the time required for visual inspection is sufficiently short, etc.).

[0108] (4) The configurations exemplified as the above-described embodiments are examples of the configurations of the present disclosure, and may be combined with other known technologies, or may be modified, such as by omitting some parts, within the scope of the gist of the present disclosure. Furthermore, the above-described embodiments may be implemented by appropriately adopting the processes and configurations described in other embodiments.

[0109] 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 by the above description, and is intended to include all modifications within the meaning and scope of the claims.

[0110] REFERENCE SIGNS LIST 11 distribution substation, 12, 13 feeder, 14 zero-phase current meter, 15a to 15h line-to-line voltage meter, 16 fault point, 17 earth capacitance, 18 branch line, 21 fault detection unit, 22 position memory unit, 31 time acquisition unit, 32 phase change calculation unit, 33 position determination unit, 34B line-to-line determination unit, 40 high-voltage single-phase distribution line, 41 single-phase pole transformer, 42 low-voltage single-phase distribution line, 43a to 43c voltage meter, 100 distribution system, 200 external device, 300 power system management device, 321 data extraction unit, 322 filter unit, 323 zero-cross time calculation unit, 324 change amount calculation unit, 331 distance acquisition unit, 332 function approximation unit, 333 change point calculation unit, 334 exception processing unit, 335A Branch line determination unit, 1000 Power system management system.

Claims

1. A power system management device for managing a power transmission and distribution system including a plurality of line voltage measuring instruments, the plurality of line voltage measuring instruments being provided at a plurality of positions on the power transmission and distribution line, the power system management device comprising: a time acquisition unit that acquires an occurrence time of a ground fault accident that occurred on the power transmission and distribution line; a phase change calculation unit that calculates an amount of phase change of the line voltages measured by each of the line voltage measuring instruments before and after the occurrence time; and a position determination unit that determines the occurrence position of the ground fault accident based on the amount of phase change of each of the line voltages.

2. The power system management device according to claim 1, wherein the position determination unit determines the location of the ground fault based on the correlation between the distance from a reference position on the power source side of the power transmission and distribution system to the position where the line voltage meter is installed and the amount of phase change of the line voltage.

3. The power system management device of claim 2, wherein when the position determination unit determines, based on the correlation, that the absolute value of the rate of change of the phase change with respect to the distance has changed from a state in which it is greater than a first threshold value to a state in which it is equal to or less than the first threshold value, it determines the location of the ground fault based on the point of change.

4. The power system management device of claim 3, wherein the position determination unit divides a section between the reference position and the position of the line voltage measuring instrument that is farthest from the reference position into a first section and a second section, calculates an intersection between a first approximation straight line derived based on the correlation in the first section and a second approximation straight line derived based on the correlation in the second section, and calculates the intersection as the changed point.

5. The power system management device according to claim 3 or claim 4, wherein the position determination unit calculates a distance from the reference position corresponding to the changed point, and if a branch line of the power transmission / distribution line exists within a first distance from the calculated distance, extracts one or more line voltage meters provided on the branch line, and extracts one line voltage meter that exists on a main line of the power transmission / distribution line and is provided at a position closest to the branch line, the phase change calculation unit calculates an amount of phase change in the line voltages measured by the one line voltage meter and each of the one or more line voltage meters before and after the occurrence time, and the position determination unit determines the occurrence position of the ground fault based on the amount of phase change in the line voltages measured by the one line voltage meter and each of the one or more line voltage meters.

6. The power system management device according to any one of claims 3 to 5, wherein when the position determination unit determines based on the correlation that the absolute value of the rate of change does not become greater than the first threshold value, it determines that the ground fault has occurred between the position of the line voltage meter closest to the reference position and the reference position.

7. The power system management device according to any one of claims 3 to 6, wherein when the position determination unit determines, based on the correlation, that the absolute value of the rate of change remains greater than the first threshold value, it determines that the ground fault has occurred at a position farther than the position of the line voltage meter that is farthest from the reference position.

8. A power system management device according to any one of claims 1 to 7, wherein the occurrence time is calculated based on a measurement value of a zero-phase sequence voltage or a zero-phase sequence current of the transmission / distribution line.

9. The power system management device according to any one of claims 1 to 8, wherein the power transmission / distribution line is a three-phase power transmission / distribution line, the phase change calculation unit calculates amounts of phase change of three line voltages measured by the line voltage measuring instrument, and the power system management device further comprises a line determination unit that identifies a first line voltage between a first phase and a second phase, a second line voltage between the second phase and a third phase, and a third line voltage between the third phase and the first phase based on the magnitudes of the phase changes of the three line voltages.

10. The power system management device according to claim 9, wherein the phase change calculation unit calculates an amount of phase change of a first voltage measured by a voltage measuring instrument provided on a single-phase distribution line drawn from the power transmission / distribution line, the position determination unit extracts a line-to-line voltage measuring instrument provided on the power transmission / distribution line and located within a second distance from the voltage measuring instrument, the phase change calculation unit calculates an amount of phase change of each of the first line voltage, the second line voltage, and the third line voltage measured by the extracted line voltage measuring instrument, and the line determination unit selects, from the first line voltage, the second line voltage, and the third line voltage, a line voltage having an amount of phase change closest to an amount of phase change of the first voltage, and determines that the first voltage has been measured between two phases corresponding to the selected line voltage.

11. A power system management system comprising: a power transmission and distribution system including a power transmission and distribution line and a plurality of line voltage measuring instruments respectively provided at a plurality of positions on the power transmission and distribution line; a detection device for detecting a ground fault in the power transmission and distribution line; and a power system management device for managing the power transmission and distribution system, wherein the power system management device includes a time acquisition unit for acquiring an occurrence time of a ground fault that occurs in the power transmission and distribution line; a phase change calculation unit for calculating an amount of phase change in the line voltages measured by each of the line voltage measuring instruments before and after the occurrence time; and a position determination unit for determining the occurrence position of the ground fault based on the amount of phase change in each of the line voltages.

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