JP2009038912A - Method and apparatus for ground fault detection - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method and an apparatus for ground fault detection wherein in three-phase, three-wire non-grounded or resistance-grounding power distribution equipment, the level of a ground fault that has occurred is known without the advance measurement of cable charging current and the relevant circuit is separated with high sensitivity before a complete ground fault results. <P>SOLUTION: The method and the apparatus are for detecting ground faults in three-phase, three-wire power distribution equipment whose ground system is of non-grounding or resistance grounding. A zero-phase voltage detection relay 8 for detecting the ground-fault voltage of an entire power distribution system and ground-fault direction relays 6, 6a, ..., 6n for detecting ground faults in individual circuits 3, 3a, ..., 3n are connected together by transmitting means 7, 7a, ..., 7n. A ground-fault resistance that will occur at a ground fault point and is to be detected is set. When the ground-fault resistance of the point of a ground fault that occurs in the power distribution system is smaller than the above set value, the circuit in which the fault has occurred is separated from the system. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a ground fault detection method and apparatus for detecting a ground fault in a three-phase three-wire power distribution facility whose grounding system is ungrounded or resistance grounded.

  In the conventional ground fault detection device of ungrounded or resistance grounding system, zero phase voltage and zero phase current generated at the time of ground fault are taken into the ground fault direction relay, and both the zero phase voltage and zero phase current values are If it is equal to or greater than the set value, the ground fault direction relay operates and trips the circuit breaker of the line where the ground fault has occurred, thereby disconnecting the ground fault point from the system (see, for example, Patent Document 1).

JP 2002-118954 A (summary column, FIG. 1)

  As described above, the conventional ground fault detection device inputs the zero phase voltage and the zero phase current when the ground fault occurs to the ground fault direction relay, and the values of both the zero phase voltage and the zero phase current are Since it is designed to operate when it exceeds the set value, the zero-phase voltage is low in a distribution system with a large ground fault current when one line is completely grounded in a three-phase three-wire distribution facility that is ungrounded or resistively grounded. There was a problem that ground faults could not be detected with high sensitivity.

  Further, if the ground fault detection device can detect the ground fault resistance, it is possible to determine how much the dielectric strength has dropped and the ground fault has progressed, and to operate the ground fault detection device. Since the ground fault detection device of No. 1 detects the zero-phase voltage and the zero-phase current generated by the accident, there is a problem that the progress degree of the ground fault can be grasped only indirectly.

  Furthermore, in the case of detecting a ground fault with high accuracy, all cable charging currents are measured in advance to set the ground fault detection device.

  The present invention has been made to solve the above-described problems. In a three-phase three-wire power distribution facility of non-grounding or resistance grounding, a ground fault that has occurred without measuring the cable charging current in advance. It is an object of the present invention to provide a ground fault detection method and apparatus for grasping the level of an accident and disconnecting the corresponding line with high sensitivity before reaching a complete ground fault.

  The ground fault detection method according to the present invention is a ground fault detection method for detecting a ground fault in a three-phase three-wire power distribution facility whose grounding system is ungrounded or resistance grounded. A zero-phase voltage detection relay that connects to a ground fault direction relay that detects a ground fault for each line by transmission means, sets the ground fault resistance to be detected at the point of the ground fault, and occurs in the power distribution system When the ground fault resistance at the ground fault point is smaller than the set value, the line in which the fault has occurred is disconnected from the system.

  The ground fault detection device according to the present invention is a ground fault detection device for detecting a ground fault in a three-phase three-wire distribution facility in which the ground system is ungrounded or resistance grounded. A zero-phase voltage detection relay for detecting a ground fault, a ground fault direction relay for detecting a ground fault for each line, and a transmission means for connecting the zero phase voltage detection relay and the ground fault direction relay, The zero-phase voltage detection relay has a calculation unit that calculates the ground fault resistance from the zero-phase voltage generated in the event of a ground fault and the zero-phase current from the above-mentioned local fault direction relay, and the ground fault resistance calculated by the calculation unit is set A ground fault resistance detection unit that outputs a signal when the value is smaller than the value; and a line cutoff command unit that outputs a ground fault line cutoff command by an output signal of the ground fault resistance detection unit.

  According to the present invention, the ground fault is detected by calculating the ground fault occurring at the ground fault point of the distribution facility having a large ground fault current at the time of the ground fault, and the ground fault resistance is set to a desired value. By operating when it reaches, it is possible to grasp the level of the ground fault that has occurred without measuring the cable charging current in advance and to disconnect the corresponding line with high sensitivity before reaching the complete ground fault.

  Exemplary embodiments of a ground fault detection method and apparatus according to the present invention will be described below in detail with reference to the accompanying drawings.

Embodiment 1 FIG.
FIG. 1 is a system configuration diagram showing a first embodiment of a ground fault detection apparatus for carrying out a ground fault detection method according to the present invention, and a first circuit breaker 2 on the secondary side of a three-phase main transformer 1. A first line 3, a second line 3 a,... N-th line 3 n configured by cables are connected to each other. A second circuit breaker 4, 4a,... 4n is connected to each of the first line 3, the second line 3a,. In addition, each of the first line 3, the second line 3a,..., The n-th line 3n includes a zero-phase current transformer 5, 5a, in series with the second circuit breakers 4, 4a,. .. 5n is provided. The ground fault direction relays 6, 6a, ... 6n are connected to the zero-phase current transformers 5, 5a, ... 5n, and the ground fault direction relays 6, 6a, ... 6n are , 7n are connected to the zero-phase voltage detection relay 8 by transmission means 7, 7a,. The ground fault direction relays 6, 6 a,... 6 n detect the zero-phase current generated at the time of the accident and the phase thereof. -118954, which is also disclosed in detail, and detailed description thereof is omitted.

  As will be described later, the zero-phase voltage detection relay 8 has an internal calculation function and is connected to the ground fault direction relays 6, 6a,... 6n by the transmission means 7, 7a,. , The value of the zero-phase current passing through the zero-phase current transformers 5, 5a,..., 5n of the first line 3, the second line 3a,. Are transmitted to the zero-phase voltage detection relay 8 through the transmission means 7, 7a,.

  Three primary windings 9a of a grounded instrument transformer (hereinafter abbreviated as EVT) 9 are Y-connected, their neutral connection points are grounded, and the other ends are connected to the first circuit breaker 2 respectively. To the secondary side of the main transformer 1. Further, the three tertiary windings 9b of the EVT 9 are broken Δ-connected, and a limiting resistor 10 is connected between the opened windings. The both ends of the limiting resistor 10 are connected to the zero-phase voltage detection relay 8 and to the ground fault direction relays 6, 6a,. In addition, the code | symbol 11, 11a, ... 11n has shown each earth | ground electrostatic capacitance of the 1st circuit | line 3, the 2nd circuit | line 3a, ... nth circuit | line 3n.

  The first embodiment of the ground fault detection apparatus for executing the ground fault detection method according to the present invention is configured as described above. Next, the operation thereof will be described with reference to FIG. FIG. 2 shows the state of the zero-phase current when a ground fault occurs. First, the principle will be described.

  The current flowing into the accident line is a vector of the effective part flowing through the limiting resistor 10 and the neutral grounding resistor (not shown) connected to the tertiary side of the EVT 9 and the ineffective part from the cable of the other healthy line Become sum. In addition, the invalid portion from the cable of the other healthy line is the zero-phase current transformer 5, 5a connected to each of the first line 3, the second line 3a,. After passing through 5n and detected by the ground fault direction relays 6, 6a,... 6n, it is obtained by the sum of data sent to the zero-phase voltage detection relay 8 by the transmission means 7, 7a,. Since the direction of the zero-phase current flowing into the fault line and the zero-phase current flowing through the healthy line are opposite to each other, the direction is determined by comparing the phase of each zero-phase current and the phase of the zero-phase voltage. It is possible to determine whether an accident has occurred.

  The ground fault resistance Rg generated at the time of the one-line ground fault and the current flowing through the zero-phase current transformer of the line where the ground fault has occurred can be obtained by the following equation (1).

However, Rg: Ground fault resistance [Ω]
E: System ground potential (when healthy) [V] (primary)
Ic: Three-phase batch system charging current [A] (Ic = 2 × π × f × C × E × 3)
Ron: Primary equivalent equivalent grounding resistance [Ω]
n: EVT turns ratio.

Among these, grid ground potential (when healthy) E, primary equivalent equivalent ground resistance value Ron, and EVT winding ratio n are values known in advance, but three-phase batch system charging current Ic is measured in advance. It is unknown because it is not performed. However, when a ground fault occurs, the cable charging current flowing from each sound line to the point of failure can be detected by a zero-phase current transformer installed in each line. The current flowing through the primary side of the EVT can be detected by a current transformer connected to the ground line of the EVT, and the fault current flowing into the fault line can be detected by a zero-phase current transformer of the fault line. The three-phase collective system charging current Ic is the sum of the cable charging current of each line, and is calculated by the following equation (2).
Ic = Ic1 + Ic2 + ... + Icn (2)

  For example, when a ground fault occurs on the first line, the cable charging current Ic1 on the first line cannot be detected by the zero-phase current transformer on the accident line. However, there are many lines in equipment where zero-phase voltage is unlikely to be generated, and the ratio of the charging current for one line to the total charging current is low. The difference in resistance is reduced and there is no particular problem.

  Next, a specific operation when a ground fault occurs in the first line 3 of FIG. 2 will be described. The cable charging current Ic1 of the first line 3 flows into the accident point and returns to the cable of the first line 3 through the ground. Cable charging currents Ic2... Icn of the other lines 3a... 3n flow toward the accident point of the first line 3 where the ground fault occurred, and each line 3a. Return to 3n.

  The current IN flowing through the limiting resistor 10 flows toward the fault point of the first line 3, and returns from the fault point to the ground of the primary winding 9a of the EVT 9 through the ground. At this time, the zero-phase current transformer 5 of the first line 3 detects the sum Ic ′ of the charging currents from the second line 3a,..., The nth line 3n and the current IN flowing through the limiting resistor 10.

  Next, the configuration and operation of the zero-phase voltage detection relay 8 will be described with reference to FIG. In FIG. 3, the zero-phase voltage detection relay 8 includes a filter 80 that is connected to both ends of the limiting resistor 10 and extracts a fundamental wave component of the zero-phase voltage, an arithmetic device 81, and an input device 82. The input device 82 inputs the set values of the resistance value of the limiting resistor 10 or a neutral grounding resistor (not shown), the tertiary voltage of the EVT 9, the line voltage, and the cable charging current to the arithmetic device 81.

  The zero-phase voltage detection relay 8 receives a signal when the ground fault resistance Rg calculated and output by the calculation device 81 is smaller than the set value of the ground fault resistance detection level set by the input device 82. A ground fault resistance detection unit 83 for outputting and a line cutoff command unit 84 for outputting a cutoff command for the corresponding line by an output signal from the ground fault resistance detection unit 83 are provided.

  The zero-phase voltage detection relay 8 is configured as described above and operates as follows. The zero-phase current data detected by the zero-phase current transformers 5, 5a,... 5n provided in the first line 3, the second line 3a,. 6, 6a,... 6n are sent to zero phase voltage detection relay 8 via transmission means 7, 7a,. Within the zero-phase voltage detection relay 8, the line where the ground fault has occurred is identified from the zero-phase current phase of each line 3, 3a... 3n, and the ground fault resistance is further determined from the zero-phase voltage and the zero-phase current. calculate. When the calculated resistance value is lower than the detection target set value, the line break command unit 84 sends a command to trip the circuit breaker of the line where the ground fault has occurred to the corresponding circuit breaker, and the ground fault point is Disconnect from.

  As described above, according to the ground fault detection method and apparatus according to the first embodiment, the relay that detects the zero-phase voltage can collect the value and phase of the zero-phase current that is detected by the local fault direction relay. It is possible to determine the sum of the zero-phase current of the sound line and the value of the zero-phase current flowing into the fault line by the sent data and calculation. The generated ground fault resistance can be obtained by calculation from the inter-voltage or the limiting resistance value. Further, the fault line is determined from the phase of the zero-phase current and the zero-phase voltage, and when the ground fault resistance falls below a predetermined value, a cutoff command can be sent to the corresponding line. Therefore, by detecting the ground fault accurately and operating when the ground fault resistance reaches the desired value, it is possible to grasp the level of the ground fault accident that has occurred without measuring the cable charging current in advance. It is possible to provide a ground fault detection method and apparatus for disconnecting a corresponding line from equipment with high sensitivity before a ground fault is reached.

  The ground fault detection method and apparatus according to the present invention are highly applicable as a ground fault detection device for detecting a ground fault in a three-phase three-wire power distribution facility whose grounding system is ungrounded or resistance grounded.

BRIEF DESCRIPTION OF THE DRAWINGS It is a system | strain block diagram which shows Embodiment 1 of the ground fault detection apparatus which enforces the ground fault detection method concerning this invention. It is a figure which shows the condition of the zero phase current at the time of a ground fault accident occurring. It is a block diagram explaining the detail of a zero phase voltage detection relay.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Three-phase main transformer 2 1st circuit breaker 3 Line 4 2nd circuit breaker 5 Zero phase current transformer 6 Ground fault direction relay 7 Transmission means, such as optical fiber 8, Zero phase voltage detection relay 9 For grounding type instruments Transformer (EVT)
DESCRIPTION OF SYMBOLS 10 Limit resistor 11 Ground capacitance 80 Filter 81 Calculation apparatus 82 Input apparatus 83 Ground fault resistance detection part 84 Line interruption | blocking command part IN Current [A] which flows by a limit resistance at the time of a ground fault
Io Ground fault current [A]
IZCT Current detected by the zero-phase current transformer on the line where the ground fault occurred [A]
Ic Total cable charging current flowing into the ground fault point [A]
Ic 'Cable charging current other than the line where the ground fault occurred [A]

Claims (2)

In a ground fault detection method for detecting a ground fault in a three-phase three-wire power distribution facility whose grounding system is ungrounded or resistance grounded,
A zero-phase voltage detection relay that detects the ground fault voltage of the entire distribution system and a ground fault direction relay that detects a ground fault accident for each line are connected by transmission means, and the ground fault resistance that is detected at the point of the ground fault is detected. A ground fault detection method characterized in that when a ground fault resistance at a ground fault point occurring in a power distribution system is smaller than the set value, the line in which the fault has occurred is disconnected from the system. In the ground fault detection device that detects a ground fault in a three-phase three-wire power distribution facility whose grounding system is ungrounded or resistance grounded,
A zero-phase voltage detection relay that detects the ground fault voltage of the entire distribution system;
A ground fault direction relay that detects ground faults for each line;
Transmission means for connecting the zero-phase voltage detection relay and the ground fault direction relay;
With
The zero-phase voltage detection relay is configured to calculate a ground fault resistance from a zero-phase voltage generated at the time of a ground fault and a zero-phase current from the local fault direction relay,
A ground fault resistance detection unit that outputs a signal when the ground fault resistance calculated by the calculation unit is smaller than a set value;
A ground fault detection device, comprising: a line cutoff command unit that outputs a ground fault line cutoff command according to an output signal of the ground fault resistance detection unit.

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