JP5256757B2 - Micro ground fault detector - Google Patents

Description

  The present invention relates to a fine ground fault detection device, and is particularly suitable for application to a method for detecting a fine ground fault that is a sign before a ground fault occurs.

  The high-voltage distribution system is managed by connecting a plurality of branch wirings called feeders to a plurality of buses connected to a power source, and providing a breaker for each feeder. In such a high voltage distribution system, a ground fault may occur due to insulation degradation of the high voltage cable or the like. As a countermeasure against this ground fault, in a conventional power system, a ground fault protection relay is provided in the high-voltage distribution system, and the fault equipment is disconnected from the system when a ground fault occurs. This ground fault protection relay detects the zero-phase voltage and zero-phase current of the equipment to be protected, both of which exceed the reference level, and the phase difference between the zero-phase voltage and zero-phase current is within a predetermined range. When a state indicating that a ground fault has occurred on the own equipment side continues for a certain period of time, it is determined as a ground fault and a trip operation is performed.

FIG. 8 is a block diagram showing a schematic configuration of a power system to which a conventional ground fault countermeasure is applied.
In FIG. 8, the power system is provided with a transformer 111 that transforms a high voltage into a low voltage. The transformer 111 is connected to the high voltage wiring through the circuit breaker 112 and is connected to the low voltage wiring through the circuit breaker 113, and the neutral point of the transformer 111 is grounded through the ground resistor 115. ing. Further, a current transformer 123 for detecting a zero-phase current generated at the neutral point of the transformer 111 at the time of a ground fault is provided, and the current transformer 123 is connected to the ground fault overcurrent relay 119. For example, the transformer 111 can transform a high voltage of 154 kV to a low voltage of 22 kV.

  In addition, feeders 122 a to 122 n are connected to the low-voltage wiring side of the transformer 111, and an instrument transformer 114 is connected. And the zero phase current transformers 117a-117n which detect the zero phase current which flows into each feeder 122a-122n are provided, and the zero phase current transformers 117a-117n are connected to the ground fault direction relays 118a-118n, respectively. A ground fault overvoltage relay 120 is connected to the open delta circuit of the instrument transformer 114.

When a ground fault occurs in the power system, a zero-phase current flows at the neutral point of the transformer 111 and a zero-phase voltage is generated in the open delta circuit of the instrument transformer 114. The zero-phase current flowing to the neutral point of the transformer 111 is detected by the current transformer 123, and the detection result is input to the ground fault overcurrent relay 119 and also to the open delta circuit of the instrument transformer 114. The generated zero-phase voltage is input to the ground fault overvoltage relay 120.
The ground fault overcurrent relay 119 and ground fault overvoltage relay 120 operate the circuit breakers 112, 113, etc. when the zero phase current and zero phase voltage show abnormal values, thereby disconnecting the accident facility from the power system. can do.

  In addition, it is not necessary to perform a shut-off operation by detecting a weak voltage / current fluctuation such as a micro ground fault or a micro short circuit, and the ground fault overcurrent relay 119 and the ground fault overvoltage relay 120 do not react to prevent malfunction. The zero-phase current and zero-phase voltage when operating the current relay 119 and the ground fault overvoltage relay 120 can be set. That is, the zero-phase current and zero-phase voltage when operating the ground fault overcurrent relay 119 and the ground fault overvoltage relay 120 can be set to 30% sensitivity of the zero phase current and zero phase voltage at the time of complete ground fault.

  For example, when the ground fault overcurrent sensitivity is 22 kV and the value at the time of complete ground fault is 100 A, 30% set value = 30 A can be set. Further, if the ground fault overcurrent sensitivity is 6.6 kV or 3.3 kV and the value at the time of complete ground fault is 30 A, it can be set to 30% set value = 9 A. Also, the ground fault overvoltage sensitivity can be set to 30% set value = 30V, assuming that the value at the time of complete ground fault is 110V.

  Also, the zero-phase currents flowing through the feeders 122a to 122n at the time of occurrence of the ground fault are respectively detected by the zero-phase current transformers 117a to 117n, and the detection results are input to the ground fault direction relays 118a to 118n, respectively. . And ground fault direction relay 118a-118n can each isolate | separate the feeder 122a-122n from an electric power grid | system, when a zero phase current shows an abnormal value.

  Here, even when the zero-phase current and the zero-phase voltage show abnormal values, the location where the ground fault occurs can only be determined between the upper transformer and the lower transformer. For this reason, by providing the ground fault direction relays 118a to 118n separately from the ground fault overcurrent relay 119 and the ground fault overvoltage relay 120, the feeders 122a to 122n where the accident has occurred can be specified.

Further, for example, in Patent Document 1, a ground fault sign is detected by detecting the magnitude and phase of a predetermined frequency component of a zero phase voltage and a zero phase current obtained by Fourier transform, thereby erroneously detecting a ground fault sign. In addition to generating alarms at high speeds and leaving only the waveform data necessary for analysis of the cause of failure as a record, repair work can be quickly performed from the cause and location of the failure found by this analysis, and a ground fault A method for preventing the above is disclosed.
JP-A-6-300806

However, in the conventional power system ground fault accident countermeasures, after the ground fault accident occurs, the accident equipment is disconnected from the power system, so the ground fault does not stop without damaging the equipment where the ground fault occurred. There was a problem that the damage could be expanded by overvoltage / overcurrent.
Further, in the method disclosed in Patent Document 1, the overcurrent relay 119 and the ground fault overvoltage relay 120 are superimposed on the commercial AC voltage so that they do not react to weak voltage / current fluctuations such as a micro ground fault or a micro short circuit. The discharge waveform at the time of ground fault is directly observed. For this reason, it is necessary to detect a steep pulse waveform of several nsec to several msec, and not only there is a possibility of detection omission, but only by analyzing the pulse waveform, the occurrence location of a fine ground fault is specified. There was a problem that I could not.
Accordingly, an object of the present invention is to provide a fine ground fault detection device that makes it easy to detect a fine ground fault that is a sign before the occurrence of a ground fault accident, and that can narrow down the occurrence location of the fine ground fault. is there.

In order to solve the above-described problem, according to the fine ground fault detection device according to claim 1, a current transformer for detecting a zero-phase current generated at a transformer neutral point of a power system, and the current transformer A connected ground fault current sensor, a waveform diagnostic device for observing the current waveform detected by the ground fault current sensor to estimate the occurrence location or aspect of the ground fault, and when the ground fault occurs A fine ground fault alarm device for issuing an alarm, wherein the waveform diagnostic device includes a current waveform obtained on an equivalent circuit from a fine ground fault occurrence point to a transformer neutral point via a power cable, and the fine ground fault. Based on the comparison result with the current waveform at the time of the micro ground fault detected by the current sensor, the occurrence location or aspect at the time of the micro ground fault is estimated, and in the equivalent circuit, the resistance of the power cable and the power cable Inductance, transformer reactor and neutral grounding resistance A series circuit bets are connected in series, a capacitor of the power cable is intended to be connected in parallel to the discharge portion of the ground fault point, the fine ground絡警paper device, in the fine ground fault current sensor An alarm is generated when the detected current value continues for several milliseconds at several mA.
Further, according to the fine ground fault detection device according to claim 2, the micro ground fault current sensor for the feeder that detects a current waveform at the time of the micro ground fault generated in the feeder of the power system is provided, and the waveform diagnosis device includes: Comparison result between the current waveform obtained on the equivalent circuit from the micro ground fault occurrence point to the transformer neutral point via the power cable and the current waveform at the time of the micro ground fault detected by the micro ground fault current sensor Further, the occurrence location or aspect of the micro ground fault is estimated based on the observation result of the current waveform at the time of the micro ground fault detected by the micro ground fault current sensor for the feeder.

Further, according to the fine ground detector according to claim 3, further comprising a fine ground voltage sensor for detecting a zero-phase voltage generated in instrument transformer of the power system, the waveform diagnostic apparatus, Bichi絡A comparison result between the current waveform obtained on the equivalent circuit from the generation point to the neutral point of the transformer via the power cable and the current waveform at the time of the micro ground fault detected by the micro ground fault current sensor, the feeder Based on the observation result of the current waveform at the time of the micro ground fault detected by the micro ground fault current sensor and the observation result of the voltage waveform at the time of the micro ground fault detected by the micro ground fault voltage sensor , It is characterized by estimating the occurrence location or aspect of the tangle.
According to the fine ground fault detection device of claim 4, the micro ground fault detection device includes a coupler that detects a voltage fluctuation of each phase generated in the bus of the power system, and the waveform diagnosis device includes a power cable from the micro ground fault generation point. The comparison result of the current waveform obtained on the equivalent circuit leading to the neutral point of the transformer via the current waveform at the time of the micro ground fault detected by the micro ground fault current sensor, the micro ground fault current for the feeder Observation result of current waveform at the time of micro ground fault detected by the sensor, observation result of voltage waveform at the time of micro ground fault detected by the micro ground voltage sensor, and time of micro ground fault detected by the coupler The occurrence location or aspect of the fine ground fault is estimated based on the observation result of the voltage fluctuation .

According to the fine ground fault detection device of claim 6, the fine ground fault current sensor for the feeder that detects the current waveform at the time of the fine ground fault occurring in the feeder and the fine ground fault current sensor for the feeder are detected. And a waveform diagnosis device that estimates the occurrence location or aspect of the micro ground fault based on the observation result of the current waveform at the time of the micro ground fault.
According to the fine ground fault detection device of claim 7, a coupler that detects a voltage fluctuation of each phase that occurs on the bus of the power system at the time of the micro ground fault, and a micro ground fault that is detected by the coupler are detected. And a waveform diagnosis device that estimates the occurrence location or aspect of the micro ground fault based on the observation result of the voltage fluctuation.
According to the fine ground fault detection device of claim 8, the waveform diagnostic device observes the current waveform or voltage waveform in a range smaller than 30% sensitivity of the zero phase current or zero phase voltage at the time of complete ground fault. Thus, the occurrence location or aspect of the fine ground fault is estimated.

  As described above, according to the present invention, by detecting the current waveform at the time of a micro ground fault occurring at the neutral point of the transformer, the ground fault current generated at the micro ground fault generating point is detected in the transformer. The current waveform when returning to the sex point can be observed, and the observed current waveform can be blunted. For this reason, it is possible to detect a sign before the occurrence of a ground fault accident without observing a steep pulse waveform of several nsec to several milliseconds, and to detect a fine ground fault that is a sign before the ground fault occurs. It becomes possible to make it easy, and it becomes possible to observe the shape of a current waveform, and it becomes possible to narrow down the occurrence location of a fine ground fault.

A fine ground fault detection apparatus according to an embodiment of the present invention will be described below with reference to the drawings.
FIG. 1 is a block diagram showing a schematic configuration of a power system to which the fine ground fault detection apparatus according to the first embodiment of the present invention is applied.
In FIG. 1, the electric power system is provided with a transformer 11 that transforms a high voltage into a low voltage. The transformer 11 is connected to the high voltage wiring through the circuit breaker 12 and is connected to the low voltage wiring through the circuit breaker 13. The neutral point of the transformer 11 is connected to the neutral point grounding resistor 15. Is grounded. Further, a current transformer 23 for detecting a zero-phase current generated at the neutral point of the transformer 11 at the time of ground fault is provided, and the current transformer 23 is connected to the fine ground fault current sensor 16. For example, the transformer 11 can transform a high voltage of 154 kV to a low voltage of 22 kV. Here, the fine ground fault current sensor 16 can detect a current waveform at the time of the fine ground fault generated at the neutral point of the transformer 11.

  In addition, feeders 22 a to 22 n are connected to the low voltage wiring side of the transformer 11, and an instrument transformer 14 is connected. And the zero phase current transformers 17a-17n which detect the zero phase current which flows into each feeder 22a-22n are provided, and the zero phase current transformers 17a-17n are respectively connected to the micro ground fault current sensors 18a-18n for feeders. ing. Here, the fine ground fault current sensors 18a to 18n for the feeder can respectively detect the current waveforms at the time of the micro ground fault generated in each of the feeders 22a to 22n.

A fine ground fault voltage sensor 19 is connected to the open delta circuit of the instrument transformer 14. Here, the fine ground fault voltage sensor 19 can detect a voltage waveform generated on the bus of the power system at the time of the fine ground fault.
A coupler 20 is connected to the bus of the power system. Here, the coupler 20 can detect the voltage fluctuation of each phase that occurs on the bus of the power system at the time of a slight ground fault. Note that a capacitor can be used as the coupler 20.

  The fine ground fault detection device is provided with a waveform diagnostic device 21. The waveform diagnostic device 21 includes a fine ground fault current sensor 16, feeder fine ground fault current sensors 18a to 18n, a fine ground fault voltage sensor 19, and a coupler. 20 is connected. Here, the waveform diagnosis device 21 can estimate the occurrence location or aspect of the micro ground fault based on the observation result of the current waveform at the time of the micro ground fault detected by the micro ground fault current sensor 16. In addition, the waveform diagnosis apparatus 21 detects the micro ground faults generated in the feeders 22a to 22n based on the observation results of the current waveforms at the time of the micro ground faults detected by the micro ground fault current sensors 18a to 18n for the feeders. The occurrence location or aspect can be estimated. Further, the waveform diagnosis device 21 can estimate the occurrence location or aspect of the fine ground fault based on the observation result of the voltage waveform at the time of the fine ground fault detected by the ground fault voltage sensor 19. Further, the waveform diagnostic device 21 can estimate the occurrence location or aspect of the fine ground fault based on the observation result of the voltage fluctuation at the time of the fine ground fault detected by the coupler 20.

  When a fine ground fault occurs at any location in the power system, the fine ground fault current generated at the location where the fine ground fault occurs returns to the neutral point of the transformer 11 via a grounding point or the like. A zero-phase current flows through the neutral point of the transformer 11 and a zero-phase voltage is generated in the open delta circuit of the instrument transformer 14. Then, the zero-phase current that has flowed to the neutral point of the transformer 11 is detected by the current transformer 23 and input to the minute ground fault current sensor 16. The current waveform generated at the neutral point of the transformer 11 is detected by the fine ground fault current sensor 16, and the detection result is input to the waveform diagnostic device 21.

Further, the zero-phase voltage generated in the open delta circuit of the instrument transformer 14 at the time of occurrence of the fine ground fault is detected by the fine ground fault voltage sensor 19, and the detection result is input to the waveform diagnostic device 21.
Further, the zero-phase currents flowing through the feeders 22a to 22n when the fine ground fault occurs are respectively detected by the zero-phase current transformers 17a to 17n and input to the feeder fine ground fault current sensors 18a to 18n, respectively. And the current waveform of each feeder 22a-22n is each detected by the fine ground fault current sensors 18a-18n for feeders, and the detection result is input into the waveform diagnostic apparatus 21. FIG.

Further, the voltage fluctuation generated in each phase of the power system bus when the fine ground fault occurs is detected while the capacitor 20 is resonating with the capacitor, and the detection result is input to the waveform diagnosis device 21.
And if the current waveform at the time of a micro ground fault is input from the micro ground fault current sensor 16, the waveform diagnostic apparatus 21 will estimate the occurrence location or aspect of the micro ground fault based on the observation result of the current waveform. Here, when estimating the occurrence location or aspect of a fine ground fault from the current waveform detected by the fine ground fault current sensor 16, the waveform diagnosis device 21 is based on the 30% sensitivity of the zero-phase current during a complete ground fault. By observing the current waveform in a small range, it is possible to estimate the occurrence location or aspect of the micro ground fault. In addition, the waveform diagnosis device 21 detects the current waveform obtained on the equivalent circuit from the minute ground fault occurrence point to the neutral point of the transformer 11 through the power cable, and the minute detected by the minute ground fault current sensor 16. Based on the comparison result with the current waveform at the time of the ground fault, it is possible to estimate the occurrence location or aspect of the fine ground fault.

Furthermore, the waveform diagnosis device 21 can estimate the occurrence location or aspect of the fine ground fault based on the intensity of discharge by the current waveform detected by the fine ground fault current sensor 16 and the duration of the current waveform. .
For example, when the intensity of the discharge due to the current waveform detected by the fine ground fault current sensor 16 is about several A, it can be estimated that the circuit breaker is uneven (three-phase opening / closing deviation).
Further, when the intensity of the discharge due to the current waveform detected by the fine ground fault current sensor 16 is about several A, it can be estimated that the insulation deterioration (tracking or the like) of the glass has occurred.

Moreover, when the intensity of the discharge due to the current waveform detected by the fine ground fault current sensor 16 is about several A, it can be estimated that an internal abnormality such as a transformer or a capacitor has occurred.
Further, when the intensity of the discharge due to the current waveform detected by the fine ground fault current sensor 16 is about several mA, it can be estimated that an insulation abnormality on the load side (rotating machine or the like) has occurred.
Further, when the intensity of the discharge due to the current waveform detected by the fine ground fault current sensor 16 is about several μA, it can be estimated that a 22 kV cable abnormality has occurred.

  Here, by detecting the current waveform with the micro ground fault current sensor 16, the current waveform when the ground fault current generated at the micro ground fault generation point returns to the neutral point of the transformer 11 can be observed. The observed current waveform can be dulled. For this reason, it is possible to detect a sign before the occurrence of a ground fault accident without observing a steep pulse waveform of several nsec to several milliseconds, and to detect a fine ground fault that is a sign before the ground fault occurs. It becomes possible to make it easy, and it becomes possible to observe the shape of a current waveform, and it becomes possible to specify the location where a fine ground fault occurs.

Moreover, when the current waveform at the time of a micro ground fault is each input from the micro ground fault current sensors 18a-18n for feeders, the waveform diagnosis apparatus 21 will perform on each feeder 22a-22n based on the observation result of the current waveform. Estimate the occurrence location or aspect of the ground fault.
Here, by detecting the current waveform with the fine ground fault current sensors 18a to 18n for the feeder, a sign before a ground fault occurs is detected without observing a steep pulse waveform of several nsec to several msec. It is possible to easily detect a fine ground fault that is a sign before a ground fault accident occurs, and it is possible to specify the occurrence location of the fine ground fault on each of the feeders 22a to 22n. .

Moreover, when the voltage waveform at the time of a micro ground fault is input from the micro ground fault voltage sensor 19, the waveform diagnostic apparatus 21 estimates the occurrence location or aspect of the micro ground fault based on the observation result of the voltage waveform.
Here, by detecting the voltage waveform with the fine ground fault voltage sensor 19, it is possible to detect a sign before a ground fault occurs without observing a steep pulse waveform of several nsec to several msec, It becomes possible to easily detect a fine ground fault that is a sign before a ground fault occurs.

Moreover, when the voltage fluctuation at the time of a micro ground fault is input from the coupler 20, the waveform diagnostic apparatus 21 estimates the occurrence location or aspect of the micro ground fault based on the observation result of the voltage fluctuation.
Here, by detecting the voltage fluctuation generated in each phase of the bus with the coupler 20, the voltage waveform can be observed while causing the capacitor resonance, and a steep pulse waveform on the order of several nsec can be captured. Therefore, it becomes possible to monitor an abnormality such as a cable or a rotating machine provided in the power system.

FIG. 2 is a diagram showing a discharge waveform at the ground fault point P of the power system of FIG. 1 and a neutral point waveform of the transformer 11.
In FIG. 2, for example, the transformer 11 transforms a high voltage of 154 kV into a low voltage of 22 kV and has an output of 100 MVA. For example, it is assumed that the reactor value L of the transformer 11 is 0.5H, the capacitance C of each of the feeders 22a to 22n is 0.9 μF, and the resistance value R of the neutral point ground resistor 15 is 127Ω.
Then, for example, the load current I ₁ is assumed to be 1000A, at the time of normal R-phase current (also referred to as a phase current) (also referred to as b-phase current) S-phase current, (also referred to as c-phase current) T-phase current balanced, zero-phase current I ₂ generated at the neutral point of the transformer 11 becomes 0A.

On the other hand, when there is a discharge at the ground fault point P, the ground fault current generated at the ground fault point P returns to the neutral point of the transformer 11 through the grounding point and the like, and becomes the neutral point of the transformer 11. flows is zero-phase current _{I 2.}
Here, when the ground fault current is observed at the ground fault point P, an R-phase discharge waveform W1 superimposed on an AC voltage of 50 Hz is detected, and this R-phase discharge waveform W1 is a steep pulse of several nsec to several msec. It becomes a waveform.

  On the other hand, at the neutral point of the transformer 11, the R-phase discharge waveform W1 does not appear as it is, but the neutral point waveform W2 blunted due to the circuit constant of the LCR of the power system appears. The intensity of the discharge of the point waveform W2 is 5 A, and the duration is about several tens of msec. For this reason, the waveform diagnosis apparatus 21 compares the current waveform obtained on the equivalent circuit composed of the LCR of the power system with the neutral point waveform W2 without directly observing the R-phase discharge waveform W1 having a steep pulse waveform. Thus, the position of the ground fault point P or the aspect of the ground fault can be estimated, and it is possible to easily detect a fine ground that is a sign before the ground fault occurs. It is possible to identify the location where the tangle occurs.

FIG. 3 is a diagram showing an equivalent circuit from the ground fault point P of the power system of FIG. 2 to the neutral point of the transformer 11.
3, when in ground fault point P discharge occurs, flows zero-phase current I ₂ through path formed between the neutral point and the power cable of the transformer 11. Route the zero-phase current I ₂ flows may be represented by an equivalent circuit using a circuit constant of LCR of the power system.
That is, in this equivalent circuit, the resistor R1 of the power cable, the inductance L2 of the power cable, the reactor L1 of the transformer 11, and the neutral point grounding resistor 15 are connected in series. And this series circuit and the capacitor | condenser C1 of an electric power cable are connected in parallel to the discharge location of the ground fault point P.
Then, the waveform of the zero-phase current I ₂ flowing on the equivalent circuit is obtained by calculation, and compared with the waveform of the zero-phase current I ₂ detected by the fine ground-fault current sensor 16 of FIG. The position of the point P or the aspect of the ground fault can be estimated.

FIG. 4 is a diagram illustrating a fine ground fault detection range in the fine ground fault detection apparatus of FIG. 1.
In FIG. 4, when a ground fault occurs, the three-phase current / voltage balance is lost, and a zero-phase current and a zero-phase voltage are generated. Even during a slight ground fault, a zero-phase current waveform of several μA to several A and a zero-phase voltage waveform of several V to several kV are generated.
And, by detecting the zero-phase current waveform and the zero-phase voltage waveform that do not occur at normal time, by analyzing the magnitude and duration of such zero-phase current and zero-phase voltage fluctuation at the stage of fine ground fault, A large-scale ground fault can be prevented.

Here, when the occurrence location or aspect of a fine ground fault is estimated from a zero-phase current waveform or zero-phase voltage waveform that does not occur under normal conditions, the 30% sensitivity of the zero-phase current or zero-phase voltage at the time of complete ground fault By observing the zero-phase current waveform or the zero-phase voltage waveform in the small range S1, it is possible to estimate the occurrence location or aspect of the fine ground fault.
As a result, the insulation is deteriorated and the leakage current starts to flow to the ground by a few μA to a few A, and when the weak voltage fluctuation occurs, it is possible to detect at an early stage. Can be maintained and repaired.

FIG. 5 is a diagram illustrating a waveform of a zero-phase voltage detected when creeping discharge occurs in the circuit breaker according to the embodiment of the present invention.
In FIG. 5, when discharge occurs, the discharge waveform does not appear as it is at the neutral point of the transformer 11, but a waveform blunted due to the circuit constant of the LCR of the power system appears. For this reason, the waveform diagnostic apparatus 21 can estimate the abnormal part or aspect which generate | occur | produced in the circuit breaker by observing the blunted waveform.

In addition, as a site | part which becomes a factor which generate | occur | produces an abnormal voltage, the following 1) -9) can be mentioned. And the magnitude | size of the abnormal voltage to generate becomes small in order of 1) -9). For this reason, the waveform diagnostic apparatus 21 can estimate the abnormal location or aspect by observing the magnitude of the abnormal voltage.
1) Non-uniformity of circuit breakers at the end of the cable 2) Non-uniformity of capacitor components and ignition of the drive device 3) Harmonic wave 4) Creeping discharge such as glass 5) Internal discharge of oil-filled transformer 6) Accessories of PT Internal discharge 7) Discharge of rotating machines and dry transformers 8) Partial discharge of CV cables 9) Lightning and switching surge

FIG. 6 is a block diagram showing a schematic configuration of a power system to which the fine ground fault detection apparatus according to the second embodiment of the present invention is applied.
In FIG. 6, this fine ground fault detection device is provided with a compensation circuit 24 that attenuates the vibration of the current waveform at the time of the fine ground fault, in addition to the configuration of FIG. 1, and the compensation circuit 24 is a neutral point of the transformer 11. It is connected to the. Note that the compensation circuit 24 can be used for apparently converting a small-scale power system to a large-scale power system, and can be configured by, for example, an LCR circuit.

When a fine ground fault occurs at any location in the power system, the fine ground fault current generated at the location where the fine ground fault occurs returns to the neutral point of the transformer 11 via a grounding point or the like. When a zero-phase current flows to the neutral point of the transformer 11, the zero-phase current flows to the neutral point grounding resistor 15 through the compensation circuit 24, and is detected by the current transformer 23. Input to the ground fault current sensor 16. The current waveform generated at the neutral point of the transformer 11 is detected by the fine ground fault current sensor 16, and the detection result is input to the waveform diagnostic device 21.
Here, by detecting the zero-phase current flowing through the neutral point of the transformer 11 by the micro ground fault current sensor 16 through the compensation circuit 24, the current waveform in which the vibration is attenuated can be observed. The current waveform can be easily observed regardless of the scale of the power system.

FIG. 7 is a block diagram showing a schematic configuration of a power system to which the fine ground fault detection device according to the third embodiment of the present invention is applied.
In FIG. 7, the electric power system is provided with a transformer 31 that transforms a high voltage into a low voltage. The transformer 31 is connected to the high voltage wiring via the circuit breaker 32 and connected to the low voltage wiring via the circuit breaker 33, and the neutral point of the transformer 31 is connected to the neutral point grounding resistor 35. Is grounded. In addition, a current transformer 43 for detecting a zero-phase current generated at the neutral point of the transformer 31 at the time of a ground fault is provided, and the current transformer 43 is connected to the micro ground fault current sensor 36 and a ground fault overcurrent. The relay 52 is connected. The fine ground fault current sensor 36 is connected to the fine ground fault alarm device 51. For example, the transformer 31 can transform a high voltage of 154 kV to a low voltage of 22 kV.

  Here, the fine ground fault current sensor 36 can detect a current waveform at the time of the fine ground fault generated at the neutral point of the transformer 31. The fine ground fault alarm device 51 can issue a warning when, for example, the zero-phase current detected by the fine ground fault current sensor 36 continues for several milliseconds at several mA. Further, the ground fault overcurrent relay 52 can perform a trip operation with a sensitivity of 30% of the zero-phase current at the time of complete ground fault. For example, when the value at 22 kV and the complete ground fault is 100 A, the current transformer When the zero-phase current detected at 43 reaches 30 A, the circuit breakers 32 and 33 can be operated.

  Moreover, the feeders 42a-42n are connected to the low voltage | pressure wiring side of the transformer 31 via the circuit breakers 44a-44n, respectively. And the zero phase current transformers 37a-37n which detect the zero phase current which flows into each feeder 42a-42n are provided, and the zero phase current transformers 37a-37n are respectively connected to the micro ground fault current sensors 38a-38n for feeders. And connected to ground fault direction relays 54a to 54n, respectively. Further, the feeder ground fault current sensors 38 a to 38 n are connected to the ground fault alarm device 53.

Here, the fine ground fault current sensors 38a to 38n for the feeder can respectively detect the current waveforms at the time of the micro ground fault generated in each of the feeders 42a to 42n. The fine ground fault alarm device 53 can issue an alarm when, for example, the zero-phase current detected by any one of the fine ground fault current sensors 38a to 38n for the feeder continues at 100 mA for 100 msec or longer. Further, the ground fault direction relays 54a to 54n can each perform a trip operation with a sensitivity of 30% of the zero phase current at the time of complete ground fault. For example, when the value at the time of complete ground fault is 22A and 100A, When the zero-phase currents detected by the zero-phase current transformers 37a to 37n reach 30A, the circuit breakers 44a to 44n can be operated.
A coupler 40 is connected to the bus of the power system. Here, the coupler 40 can detect the voltage fluctuation of each phase that occurs on the bus of the power system at the time of a slight ground fault. As the coupler 40, a capacitor can be used.

  The fine ground fault detection device is provided with a waveform diagnostic device 41, and the fine ground fault alarm devices 51 and 53 and the coupler 40 are connected to the waveform diagnostic device 41. Here, the waveform diagnosis device 41 can estimate the occurrence location or aspect of the micro ground fault based on the observation result of the current waveform at the time of the micro ground fault output from the micro ground fault alarm device 51. Further, the waveform diagnosis device 41 estimates the occurrence location or aspect of the micro ground fault generated in each of the feeders 42a to 42n based on the observation result of the current waveform at the time of the micro ground fault output from the micro ground fault alarm device 53. can do. In addition, the waveform diagnosis apparatus 41 can estimate the occurrence location or aspect of the micro ground fault based on the observation result of the voltage fluctuation at the time of the micro ground fault detected by the coupler 40.

  Then, when a fine ground fault occurs at any location in the power system, the fine ground fault current generated at the location where the fine ground fault occurs returns to the neutral point of the transformer 31 via a grounding point or the like. When a zero-phase current flows through the neutral point of the transformer 31, the zero-phase current flowing through the neutral point of the transformer 31 is detected by the current transformer 43 and input to the fine ground fault current sensor 36. . Then, the current waveform generated at the neutral point of the transformer 31 is detected by the fine ground fault current sensor 36, and the detection result is input to the fine ground fault alarm device 52 and via the fine ground fault alarm device 52. Are input to the waveform diagnosis device 41.

  Then, when the current waveform at the time of the micro ground fault is input from the micro ground fault current sensor 36, the micro ground fault alarm device 52 receives the zero phase current detected by the micro ground fault current sensor 36 at several mA and several msec. It is determined whether or not it has been continued, and an alarm is issued when the zero-phase current continues for several milliseconds at several mA. Moreover, when the current waveform at the time of a micro ground fault is input from the micro ground fault alarm device 52, the waveform diagnosis apparatus 41 estimates the occurrence location or aspect of the micro ground fault based on the observation result of the current waveform.

  Also, the zero-phase currents that flow through the feeders 42a to 42n when a fine ground fault occurs are detected by the zero-phase current transformers 37a to 37n, respectively, and input to the feeder fine ground fault current sensors 38a to 38n, respectively. The current waveforms of the feeders 42a to 42n are respectively detected by the feeder ground fault current sensors 38a to 38n, and the detection results are input to the ground fault alarm device 53. Is input to the waveform diagnosis apparatus 41 via

  When the current waveform at the time of the micro ground fault is input from the micro ground fault current sensors 38a to 38n for the feeder, the micro ground fault alarm device 53 detects the zero detected by the micro ground fault current sensors 38a to 38n for the feeder. It is determined whether the phase current has continued for 100 msec or more at 100 mA, and an alarm is issued when the zero-phase current has continued for 100 msec or more at 100 mA. Further, when the current waveform at the time of the micro ground fault is input from the micro ground fault alarm device 53, the waveform diagnosis apparatus 41 detects the micro ground fault on each of the feeders 42a to 42n based on the observation result of the current waveform. Estimate the location or appearance.

Further, the voltage fluctuation generated in each phase of the bus of the power system at the time of occurrence of the fine ground fault is detected while the capacitor 40 is resonating with the capacitor, and the detection result is input to the waveform diagnosis device 41. And if the voltage fluctuation at the time of a micro ground fault is input from the coupler 40, the waveform diagnostic apparatus 41 will estimate the occurrence location or aspect of a micro ground fault based on the observation result of the voltage fluctuation.
Further, the detected value of the zero-phase current detected by the current transformer 43 is input to the ground fault overcurrent relay 52. Then, the ground fault overcurrent relay 52 determines whether or not the zero-phase current detected by the current transformer 43 exceeds 30 A, and when the zero-phase current exceeds 30 A, the circuit breakers 112 and 113 are operated. In this way, the accident equipment is disconnected from the power system.

Moreover, the detected value of the zero phase current detected by each of the zero phase current transformers 37a to 37n is input to the ground fault direction relays 54a to 54n, respectively. Then, the tangential direction relays 54a to 54n determine whether the zero phase current detected by the zero phase current transformers 37a to 37n has exceeded 30A. If the zero phase current exceeds 30A, By operating the devices 44a to 44n, the accident facility is disconnected from the power system.
This makes it possible to easily detect a micro ground fault that is a sign of a ground fault before it occurs, identify the location of the micro ground fault, and disconnect the accident equipment from the system when a ground fault occurs. It is possible to prevent the expansion of damage caused by the occurrence of a ground fault, and it is possible to maintain or repair an abnormal part before a serious ground fault occurs.

It is a block diagram which shows schematic structure of the electric power system with which the fine ground fault detection apparatus which concerns on 1st Embodiment of this invention was applied. It is a figure which shows the discharge waveform in the ground fault point P of the electric power system of FIG. 2, and the neutral point waveform of the transformer 11. FIG. It is a figure which shows the equivalent circuit from the ground fault point P of the electric power system of FIG. 1 to the neutral point of the transformer 11. FIG. It is a figure which shows the fine ground fault detection range in the fine ground fault detection apparatus of FIG. It is a figure which shows the waveform of the zero phase voltage detected when creeping discharge generate | occur | produced in the circuit breaker which concerns on one Embodiment of this invention. It is a block diagram which shows schematic structure of the electric power system with which the fine ground fault detection apparatus which concerns on 2nd Embodiment of this invention was applied. It is a block diagram which shows schematic structure of the electric power system with which the fine ground fault detection apparatus which concerns on 3rd Embodiment of this invention was applied. It is a block diagram which shows schematic structure of the electric power grid | system to which the conventional ground fault accident countermeasures were applied.

Explanation of symbols

11, 31, 111 Transformer 12, 13, 32, 33, 112, 113 Breaker 14, 114 Instrument transformer 15, 35, 115 Neutral grounding resistor 16, 36 Micro ground fault current sensor 18a-18n, 38a to 38n Feeder fine ground fault current sensor 17a to 17n, 37a to 37n, 117a to 117n Zero phase current transformer 19 Micro ground fault voltage sensor 20, 40 Coupler 21, 41 Waveform diagnostic device 22a to 22n, 122a to 122n Feeder 24 Compensation circuit 51, 53 Micro ground fault alarm device 52, 119 Ground fault overcurrent relay 54a-54n, 118a-118n Ground fault direction relay L1 Reactor R1 Resistance L2 Inductance C1 Capacitor 23, 43, 123 Current transformer

Claims (4)

A current transformer for detecting a zero-phase current generated at a transformer neutral point of a power system; a fine ground fault current sensor connected to the current transformer; and a current waveform detected by the fine ground fault current sensor A waveform diagnosis device that estimates the occurrence location or aspect of a micro ground fault and a micro ground fault alarm device that issues an alarm when the micro ground fault occurs,
The waveform diagnosis apparatus is configured to obtain a current waveform obtained on an equivalent circuit from a micro ground fault occurrence point to a transformer neutral point via a power cable, and a micro ground fault detected by the micro ground fault current sensor. Based on the comparison result with the current waveform, the occurrence location or aspect at the time of the micro ground fault is estimated, and in the equivalent circuit, the resistance of the power cable, the inductance of the power cable, the reactor of the transformer, and the neutral point A series circuit in which a grounding resistor is connected in series and a capacitor of the power cable are connected in parallel to the discharge point of the ground fault point,
The fine ground fault alarm device generates an alarm when the current value of the current detected by the micro ground fault current sensor continues for several milliseconds at several mA.   Provided with a fine ground fault current sensor for a feeder that detects a current waveform at the time of a micro ground fault occurring in a feeder of the power system, the waveform diagnosis device is a transformer neutral point via a power cable from the micro ground fault occurrence point The comparison result of the current waveform obtained on the equivalent circuit leading to the current waveform and the current waveform at the time of the micro ground fault detected by the micro ground fault current sensor and the micro ground detected by the micro ground fault current sensor for the feeder 2. The fine ground fault detection apparatus according to claim 1, wherein the occurrence location or aspect of the fine ground fault is estimated based on an observation result of a current waveform at the time of the fault.   A fine ground fault voltage sensor for detecting a zero-phase voltage generated in an instrument transformer of the power system is provided, and the waveform diagnosis device is equivalent to a transformer neutral point via a power cable from a fine ground fault occurrence point. The comparison result of the current waveform obtained on the circuit and the current waveform at the time of the micro ground fault detected by the micro ground fault current sensor, the time of the micro ground fault detected by the micro ground fault current sensor for the feeder The location or aspect of occurrence of the fine ground fault is estimated based on the observation result of the current waveform and the observation result of the voltage waveform at the time of the fine ground fault detected by the fine ground fault voltage sensor. The fine ground fault detection apparatus according to 2.   Provided with a coupler that detects voltage fluctuation of each phase generated on the bus of the power system, the waveform diagnosis device was obtained on an equivalent circuit from the point of occurrence of a micro ground fault to the neutral point of the transformer via the power cable Comparison result of current waveform and current waveform at the time of micro ground fault detected by the micro ground fault current sensor, observation result of current waveform at the time of micro ground fault detected by the micro ground fault current sensor for feeder The occurrence of the micro ground fault based on the observation result of the voltage waveform at the time of the micro ground fault detected by the micro ground fault voltage sensor and the observation result of the voltage fluctuation at the time of the micro ground fault detected by the coupler. The fine ground fault detection apparatus according to claim 3, wherein a location or an aspect is estimated.

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