JP2013113632A - Ground fault detecting method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a ground fault detecting method for easily identifying a feeder wire where an intermittent ground fault occurs.SOLUTION: The ground fault detecting method in a power distribution system where a plurality of feeder wires 2, 3, 4 are connected to a bus line 1 and zero-phase current transformers ZCT are provided for the respective feeder wires 2, 3, 4 measures secondary side terminal voltage of the zero-phase current transformers ZCT and detects the feeder wire 2 to which ground fault occurs on the basis of the measured terminal voltage. Also, the ground fault detecting method has a relay DG operating by the secondary side current of the zero-phase current transformers ZCT and detects a feeder wire to which a ground fault occurs on the basis of the secondary-side terminal voltage when the relay DG is in a non-operation state.

Description

  The present invention relates to a ground fault detection technique for detecting a feeder line in which a ground fault has occurred from a plurality of feeder lines.

In the power distribution system, a plurality of feeder lines are branched and connected to one bus, and a protection circuit for protecting the power distribution system is incorporated. When the occurrence of a ground fault is detected, the protection circuit changes the AC breaker CB of the feeder line that has detected the ground fault to a cutoff state to protect the power distribution system.
The protection circuit includes a ground fault overvoltage relay (0VG) that detects an increase in zero phase voltage due to a ground fault from the bus voltage, a zero phase current transformer (ZCT) provided on each feeder line, and a zero phase current transformer. A ground fault direction relay (DG) that specifies a feeder line (hereinafter also referred to as a ground fault feeder) grounded from the direction of each feeder line zero-phase current due to a ground fault based on the current from the unit.

  As a method for protecting a power distribution system by specifying a feeder line in which the ground fault has occurred, there is a technique described in Patent Document 1, for example. In this prior art, a ground fault overvoltage relay detects a zero-phase voltage increase due to a ground fault, and further, based on detection of a ground fault direction relay, a feeder line that is grounded from the direction of each feeder line zero-phase current due to a ground fault The ground fault feeder is specified by the AND condition of the two conditions of detecting, and the power distribution system is protected by cutting off the specified ground fault feeder.

JP-A-6-70448

However, in the power distribution system as described above, even if a ground fault overvoltage relay (0VG) detects a zero-phase voltage rise in the state of a minute intermittent ground fault before a complete ground fault, a local fault is detected. In many cases, the directional relay (DG) does not operate. In such a case, “which feeder line is grounded” cannot be specified.
At present, when identifying feeder lines that have this minute intermittent ground fault, perform a precise survey of each feeder line by temporarily shutting down each feeder line before the complete ground fault occurs. There was a need. Or it waited until a complete ground fault was reached, and the ground fault point was confirmed through DG operation (= breaker trip).

However, such a method has problems such as causing a long-time power failure of a sound facility, or causing a facility power failure due to a power failure suddenly due to a circuit breaker trip.
The present invention has been made paying attention to the above points, and an object thereof is to provide a ground fault detection technique that can more easily specify a feeder line in which an intermittent ground fault has occurred.

In order to solve the above-mentioned problems, the invention described in claim 1 of the present invention is a distribution system in which a plurality of feeder lines are connected to a bus and a zero-phase current transformer is provided for each feeder line. The ground fault detection method is characterized in that a secondary terminal voltage of the zero-phase current transformer is measured, and a feeder line in which a ground fault occurs is detected based on the measured terminal voltage.
Next, the invention described in claim 2 has a relay that operates with the secondary current of the zero-phase current transformer in the configuration described in claim 1, and generates a ground fault from the zero-phase voltage of the bus. In the ground fault detection method for detecting a feeder line in which a ground fault occurs due to the operation of the relay by the zero phase current detected by each zero phase current transformer,
When the relay is in a non-operating state, a feeder line having a ground fault is detected based on the terminal voltage.

Next, the invention described in claim 3 has a relay to which the secondary side current of the zero-phase current transformer is input to the configuration described in claim 1 or claim 2,
The secondary terminal voltage of the zero phase current transformer is measured using the impedance of the relay.

  According to the present invention, even in a power distribution system that eliminates a ground fault in a distribution line by satisfying the conditions of both a ground fault overvoltage relay and a ground fault direction relay, the ground fault direction relay does not lead to operation. It is possible to easily detect a feeder line in which a ground fault has occurred.

It is a figure which shows an example of the power distribution system which concerns on embodiment based on this invention. It is a figure explaining the flow of the electric current at the time of a ground fault generating. It is a figure which shows the state of the voltage at the time of causing a ground fault artificially with a specific feeder line.

Next, embodiments of the present invention will be described with reference to the drawings.
FIG. 1 is a diagram illustrating an example of a power distribution system according to the present embodiment.
In the power distribution system of this embodiment, as shown in FIG. 1, three feeder lines 2, 3, and 4 are branched with respect to one bus 1, and a grounding transformer GPT is connected to the bus 1. This is an example.
An AC circuit breaker CB and a zero-phase current transformer ZCT are provided in series for each feeder line 2, 3 and 4, respectively. Reference DG is a ground fault direction relay.
The AC circuit breaker CB has a function of cutting off the corresponding feeder wires 2, 3 and 4 from the bus 1.

  The zero-phase current transformer ZCT has a primary-side winding as a three-phase conductor, and the vector sum of each phase current is zero at all times or at the time of a short circuit failure, so no current flows on the secondary side. On the other hand, if a ground fault occurs in any feeder line 2, the primary side of each zero-phase current transformer ZCT is also connected to the electrostatic capacity on the load side from the installation location even in the event of a ground fault occurring in a place other than the protection duty section. A shunt of the ground fault current flows through the capacity. At this time, in the feeder line 2 (ground fault feeder) in which the ground fault has occurred, the ground fault current circulates through the ground capacitance of the cable and is combined with the ground charging currents of the other feeder lines 3 and 4 in FIG. Such a current flow is temporarily formed. For this reason, the neutral point current (zero-phase current) flowing on the secondary side of the zero-phase current transformer of each feeder is reversed in the direction of flow between the ground fault feeder 2 and the other feeder lines 3 and 4. The example of FIG. 2 is a case of a non-grounding system, but in the grounding system, a circuit in which the ground fault current returns from the grounding point is obtained.

The grounding transformer GPT is provided in a distribution substation or the like, and the connection operates the ground fault overvoltage relay (0VG) with the generation voltage (zero phase voltage) of the third order open delta. In addition, a third-order limiting resistor is inserted to stabilize the neutral point, and a complete ground fault current in a state without ground capacitance is determined. In the present embodiment, the zero-phase voltage is detected by the grounded-type instrument transformer 6 (zero-phase voltmeter) as the ground fault overvoltage relay (0VG). There is no problem even if a ground fault overvoltage relay (0VG) is used.
The ground fault direction relay DG detects the presence or absence of a ground fault from the phase relationship between the zero phase current, which is the secondary current of the zero phase current transformer ZCT, and the zero phase voltage detected by the grounded instrument transformer 6. In the case of a fault detection, the corresponding AC circuit breaker CB is operated to selectively cut off the ground fault feeder.

Furthermore, in this embodiment, the voltage measurement oscilloscope 5 for ground fault detection is provided. The sampling frequency of the oscilloscope 5 is about 10 kHz, for example. The sampling frequency of the oscilloscope 5 is preferably set higher than the sampling frequency of the ground fault direction relay DG.
The oscilloscope 5 inputs the zero-phase voltage detected by the grounded-type instrument transformer 6 and is connected in parallel to the secondary side of each zero-phase current transformer ZCT to connect the secondary side of each zero-phase current transformer ZCT. The secondary side terminal voltage corresponding to the zero-phase current flowing through is detected. The zero-phase voltage and the secondary terminal voltage of each zero-phase current transformer ZCT are displayed on the screen in time series, and the time-series data is stored in the recording device.

Then, when it is detected that the zero-phase voltage is relatively steep based on the display screen output from the oscilloscope 5 and the recording of the recording device, it is determined that a ground fault has occurred, and further, each ground fault is detected. The direction of the peak of the secondary side terminal voltage is compared, and the feeder line 2 corresponding to the secondary side terminal voltage whose phase rises in the opposite phase to the other secondary side terminal voltage is specified as the ground fault feeder. And the AC circuit breaker CB of the feeder line 2 identified as the ground fault feeder is interrupted.
At this time, when the ground fault direction relay DG is operated and the AC circuit breaker CB of the feeder line 2 specified as the ground fault feeder is cut off, the zero side voltage and the secondary side terminal of each zero phase current transformer ZCT There is no need to determine the ground fault feeder by voltage.

(Action and others)
In this embodiment, the zero-phase voltage (bus 10VG) of the distribution system is detected, but each feeder line 2, 3 is in a state where the ground fault direction relay DG is not activated by the zero-phase current of the feeder lines 2, 3, 4. , 4 measure the secondary terminal voltage of the zero-phase current transformer ZCT. The zero-phase current detected by the zero-phase current transformer ZCT has a direction, and the direction of the zero-phase current is opposite between the ground fault feeder and the non-ground fault feeder. At this time, the direction of the voltage induced at the secondary terminal of the zero-phase current transformer ZCT by the zero-phase current is also reversed by the ground / non-ground-fault feeder. Therefore, by measuring the voltage at this terminal, It is possible to identify feeder lines 2, 3, and 4 in which entanglement has occurred.
Here, the voltage induced at the secondary side terminal of the zero phase current transformer ZCT is induced by the impedance of the zero phase current flowing on the secondary side of the zero phase current transformer ZCT and the ground fault direction relay DG. .

In FIG. 1, the ground fault current If flowing through the ground fault point F is the sum of the ground fault current In flowing from the line including the ground fault point and the ground fault current lc flowing from the other line. Therefore, the direction of the zero-phase current detected by the ZCT attached to each line is reversed between the ground fault line and the non-ground fault line.
Here, the zero phase current detected by the zero phase current transformer ZCT fluctuates due to radio noise or the like. For this reason, considering that the zero-phase current is detected more accurately and the occurrence of a minute intermittent ground fault is considered, a separate resistor is inserted in series on the secondary side of the zero-phase current transformer ZCT and a current sensor is used. It is necessary to measure. In this case, however, the sensitivity of the zero-phase current is reduced by the impedance of the interrupted resistor. Moreover, since it is necessary to disconnect and interrupt once, it is necessary to once interrupt the corresponding protection duty section.

  On the other hand, in this embodiment, since the voltage induced at the secondary side terminal is measured, there is no need for disconnection, and the parallel connection to the secondary side terminal causes a reduction in the zero-phase current. There is nothing. That is, in the present embodiment, the voltage value to be measured can be detected accurately and easily. That is, it is possible to detect only the direction of the zero-phase current with high accuracy by omitting the modification work by detecting the voltage element.

  Here, in order to detect the ground fault feeder, it is necessary to detect the direction of each feeder line 2, 3, 4 zero-phase current with a finer accuracy than the operation of the ground fault direction relay DG. For this reason, in this embodiment, in order to detect a minute intermittent ground fault in which the ground fault direction relay DG does not operate, the oscilloscope 5 having a sampling frequency of about 10 kHz is used. The measurement terminal is attached to the secondary side of the ZCT, but it is desirable to measure near the DG relay for safety.

  As described above, in the ground fault detection method of the present embodiment, there is no need for a power failure of the equipment and no need to approach the high-voltage charging unit, so that it is safe and quick at the moment when the zero-phase voltage due to the ground fault comes out. It is possible to determine the ground fault feeder. For this reason, it is possible to avoid the “loss of work due to a power outage and loss due to a power outage” and “equipment / opportunity loss due to a ground fault trip” that have occurred in the past, and to find the failure point early. By doing so, it is possible to minimize equipment deterioration.

  Here, in the above embodiment, when the occurrence of the ground fault is detected from the zero-phase voltage of the bus 1, the direction of the voltage induced at the secondary side terminal of the zero-phase current transformer ZCT is reversed. The case where the feeder line 2 corresponding to the current transformer ZCT is determined as a ground fault feeder has been illustrated. As can be seen from FIG. 3, the voltage induced at the secondary side terminal of the ground fault feeder is larger than the voltage induced at the secondary side terminal of the other ground fault feeder, so that it is induced at the secondary side terminal. The feeder line 2 having the largest voltage (or the feeder line 2 having the largest ratio to the preceding and following voltage values) may be determined as the ground fault feeder.

Moreover, although the said embodiment illustrated the case where the ground fault feeder is detected by detecting and comparing the zero-phase voltage and each secondary terminal voltage with the oscilloscope 5, it is not limited to this. Detection of the ground fault feeder may be automatically determined based on the time series data of each voltage.
For example, when it is detected that the detected zero-phase voltage and each secondary terminal voltage are preset and acquired and stored in a sampling period while the detected zero-phase voltage is equal to or higher than a preset ground fault detection voltage. The peak voltage of each secondary terminal voltage detected before and after the rising time of the zero-phase voltage when the ground fault detection voltage is exceeded is acquired, and the direction or magnitude of the peak voltage of the secondary terminal voltage is acquired. Based on this, the feeder corresponding to the secondary terminal voltage having a voltage value that is opposite in phase or different in magnitude from the other secondary terminal voltage is determined as a ground fault feeder, and a cutoff operation signal is sent to the AC circuit breaker CB of the ground fault feeder. Output.

1 Busbar 2, 3, 4 Feeder 2 Ground fault feeder 5 Oscilloscope 6 Grounding-type instrument transformer CB AC circuit breaker DG Ground fault direction relay GPT Ground transformer ZCT Zero-phase current transformer If Ground fault current In Ground fault current lc Earth fault current

Claims (3)

A ground fault detection method in a distribution system in which a plurality of feeder lines are connected to a bus line and a zero-phase current transformer is provided for each feeder line,
A ground fault detection method comprising measuring a secondary terminal voltage of the zero-phase current transformer and detecting a feeder line in which a ground fault is generated based on the measured terminal voltage. It has a relay that operates with the secondary current of the zero-phase current transformer, determines the occurrence of ground fault from the zero-phase voltage of the bus, and operates the relay with the zero-phase current detected by each zero-phase current transformer In the ground fault detection method for detecting a feeder line where a ground fault has occurred,
2. The ground fault detection method according to claim 1, wherein when the relay is in an inoperative state, a feeder line in which a ground fault occurs is detected based on the terminal voltage. A relay to which a secondary current of the zero-phase current transformer is input;
The ground fault detection method according to claim 1 or 2, wherein the measurement of the secondary side terminal voltage of the zero-phase current transformer is detected by using the impedance of the relay.

Images