JPH04236124A - Method for detecting small ground fault of high-voltage distribution line - Google Patents

Abstract

PURPOSE:To provide a method for detecting the small ground-fault of a high- voltage distribution line by not disconnecting other sound distribution lines, but selectively disconnecting the faulty line only. CONSTITUTION:A directional grounding device 10 which detects the three-phase voltage of a bus 1 and three-phase current of distribution lines 2a-2f when the system is sound and is constituted as a microcomputer which functions as the directional relay of each distribution line selects the distribution line in which a small ground fault occurs in such a way that the input of the directional ground relay of each distribution line is obtained by finding the vector zero-phase voltage and current VO' and IO' of the system and the vector difference VOF' and IOF' before and after the accidents of the zero-phase voltage and current occur and such sensitivity switching that the sensitivity of each directional relay is returned to its ordinary level after the sensitively is once switched to a high level when the relay is not actuated is successively performed on each directional relay.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for detecting a slight ground fault line in a high-voltage distribution line for selectively shutting off a slight ground fault line in a power distribution system.

0002

2. Description of the Related Art Conventionally, detection of a faulty ground fault line in a power distribution system has been carried out using directional ground fault relays and slight ground fault relays. If a constant ground fault fault current IOF and a zero-sequence voltage VOF caused by the ground fault occur, the directional ground fault relay can correctly select the fault line (distribution line) and issue a disconnection command depending on the direction of the fault current IOF.

By the way, when the system is healthy, the residual zero-sequence current I
O′ and residual zero-sequence voltage VO′ are generated, and this residual zero-sequence current,
As shown in FIG. 5, the voltages IO' and VO' have arbitrary magnitudes and phases, so that in these magnitudes and phases, fault currents and voltages that occur at the time of a slight ground fault are canceled out or phase-shifted. Therefore, directional ground fault relays cannot be made highly sensitive.

[0004] For this reason, in the case of a minor ground fault accident, the directional ground fault relay does not operate, so conventionally a method has been used in which the distribution lines are sequentially cut off and on by the operation of the slight ground fault relay.

Referring to FIG. 4, the method of detecting a slight ground fault line that is currently generally employed detects a slight ground fault by the operation of a slight ground fault relay VG connected to the ground voltage detection transformer GPT provided on the bus 1. When detected, for example, circuit breaker CBa,
The power is cut off in the order of CBb..., and the distribution lines 2a, 2b... are disconnected until the ground fault voltage VOF disappears.

In the case of FIG. 4, since the slight ground fault F has occurred in the distribution line 2d, the zero-sequence voltage V does not change until the distribution line 2d is cut off.
The OF disappears, and it can be seen that this distribution line 2d is the faulty line. Therefore, leaving only the distribution line 2d, the circuit breakers CBa, CBb, and CBc of the other disconnected distribution lines 2a, 2b, and 2c
and restore it.

[0007]

The above-mentioned conventional method for detecting faulty lines due to slight ground faults involves sequential interruption of distribution lines, and therefore has the following drawbacks.

(1) A healthy power distribution line will be temporarily out of power. For example, if the power distribution line 2f in FIG. 4 is a faulty line, all lines will be cut off.

(2) The sequence of successive shutdowns is complex and causes a decrease in the reliability of the entire device.

(3) Accident removal time becomes longer.

(4) The number of times the circuit breaker operates increases, reducing the lifespan of the equipment.

[0012] The present invention has been made in view of the above-mentioned conventional problems, and its purpose is to prevent a slight ground fault in a high-voltage power distribution line by selectively interrupting the distribution line in which a slight ground fault has occurred. This provides a method for detecting lines.

[0013]

[Means for Solving the Problems] In order to solve the above object, the method of detecting a slight ground fault fault line in a high voltage distribution line according to the present invention includes detecting the three-phase voltage of the bus bar and the three-phase voltage of each distribution line when the system is healthy.
The phase current is detected, the zero-sequence voltage of the system and the zero-sequence current of each distribution line are calculated, and the vector difference between the zero-sequence voltage and each zero-sequence current before and after the accident occurrence is calculated, respectively, and the zero-sequence voltage of each distribution line is calculated. This is used as an input for a directional ground fault relay, and the sensitivity of each directional ground fault relay is switched to high sensitivity, and if the relay does not operate, the sensitivity is returned to normal sensitivity.Sensitivity switching is performed sequentially until one of the relays operates.

[0014]

[Operation] When the system is healthy, the 3-phase voltage of the busbar and the 3-phase voltage of each distribution line
By detecting the phase current and finding the zero-sequence voltage of the system and the zero-sequence current of each distribution line, and finding the vector difference between the zero-sequence voltage and each zero-sequence current before and after the fault occurs, the zero-sequence voltage caused by the fault can be calculated. and zero-sequence current can be detected.

[0015] If the zero-sequence voltage and each phase current generated by this accident are input to each direction ground fault relay, the directional ground fault relay for healthy distribution lines will not operate even if its sensitivity is increased; The directional ground fault relay for the faulty distribution line operates by increasing its sensitivity.

[0016] Therefore, if the sensitivity of each direction ground fault relay is switched to high sensitivity and it does not operate, the distribution line is healthy, so the sensitivity is returned to normal sensitivity and the sensitivity of the next relay is switched to high sensitivity and it operates. If not, by repeating the process of returning to the normal sensitivity until one of the directional ground fault relays is activated, it is possible to selectively shut off the faulty distribution line without shutting off the healthy distribution line.

[0017]

Embodiment An embodiment of the present invention will be described with reference to FIGS. 1 to 4.

In FIG. 1, 1 is a bus bar, 2a to 2f are distribution lines connected to the bus 1 via circuit breakers CBa to CBf, and CTa to CTf are phase currents IR and IS provided in each distribution line.
, TT (hereinafter simply referred to as CTa, CTb...), PT is the phase voltage VR, VS, VT provided on bus 1.
A voltage transformer (hereinafter simply referred to as PT), 10, which receives the zero-sequence voltage and zero-sequence current of PT and CTa to CTf, uses a microcomputer that functions as a directional ground fault relay for each distribution line 2a to 2f. This is a directional ground fault relay device.

FIG. 2 shows a functional block circuit diagram of the directional ground fault relay device 10, in which 11 is an A/D converter that converts the voltage of each bus phase from the PT into a digital signal, and 12 is a CTa.
~An A/D converter that converts each phase current of each distribution line from CTf into a digital signal, and 13 is a vector sum of three-phase voltage signals VR, VS, and VT from the A/D converter 11 to calculate a vector when the system is healthy. A calculation unit 14 calculates the residual zero-sequence voltage VO′ for each distribution line when the system is healthy by the vector sum of the three-phase currents IR+IS+IT for each distribution line from the A/D converter 12. 15 is a storage section that stores the zero-sequence voltage and currents VO' and IO' obtained by the calculation units 13 and 14.

16 calculates the vector current zero-phase voltage VOF' from the vector sum of the three-phase voltages from the A/D converter 11, and calculates the vector residual zero-phase voltage stored in the storage unit 15 from this zero-phase voltage VOF'. A calculation unit that calculates a vector zero-phase voltage VOF caused by an accident as a difference between voltages VO'.

Reference numeral 17 calculates the vector current zero-sequence current IOF' by the vector sum of the three-phase currents from the A/D converter 12, and calculates the vector residual zero-sequence current IOF' stored in the storage means 15 from this current IOF'. A calculation unit that calculates the vector zero-sequence current IOF of each distribution line caused by an accident as the difference between .

18 is the zero-sequence voltage VOF obtained by the calculation unit 16
is compared with the high-sensitivity setting value, and if it exceeds this setting value, it is output to the AND circuit 21 and the storage unit 15 to stop updating of the stored vector zero-sequence voltage, current VO', IO', AND circuit 2 compared with the normal sensitivity setting value
This determination unit 18 and AN
A slight ground fault is determined by the D circuit 21. Reference numeral 19 denotes a sensitivity setting section for setting the sensitivity of the zero-phase voltage determination section.

22 is the vector zero-sequence voltage of the calculation results of the calculation units 16 and 17 based on the slight ground fault determination output of the AND circuit 21;
Sensitivity switching means for multiplying the currents VOF and IOF by coefficients to sequentially switch the sensitivity of the ground fault relays in each direction as shown in FIG.

Reference numeral 23 denotes a ground fault line discriminator which compares the phases of the vector voltages VOF and IOF obtained by switching the sensitivities of the arithmetic units 16 and 17, and outputs a trip signal for the circuit breaker of the faulty distribution line.

Since the directional ground fault relay device 10 is constructed as described above, when a slight ground fault occurs, the directional ground fault relay sensitivity of each power distribution line is first adjusted as shown in FIG. Switch the relay on the power line 2a to high sensitivity, and if that relay does not operate, return the relay sensitivity to the original normal sensitivity so that it does not operate, then switch the relay on the distribution line 2b to high sensitivity, and then switch the relay to high sensitivity. When the relay does not operate, the sensitivity of the relay is returned to its original value, and then the relay of the next distribution line 2c is set to high sensitivity.If the sensitivity is switched sequentially, the relay can be switched off without interrupting the distribution lines 2a, 2b, and 2c. , it is possible to selectively shut off the relay of the distribution line 2d where the accident has occurred.

In the above embodiment, in order to obtain the zero-sequence voltage,
Although the vector phase voltage is used, it can also be determined using the line voltage using the vector line voltage VR-S as a reference, for example.

[0027]

[Effects of the Invention] Since the present invention is constructed as described above, it produces the following effects.

(1) A directional ground fault relay can selectively cut off a slight ground fault distribution line.

(2) Unlike the conventional sequential cut-off method using a slight ground fault relay, there is no need to test cut off the distribution lines and cause a power outage to healthy distribution lines.

[Brief explanation of the drawing]

FIG. 1 is a system configuration diagram according to an embodiment of the present invention.

FIG. 2 is a functional block diagram of a directional ground fault relay device according to an embodiment of the present invention.

FIG. 3 is an explanatory diagram of sensitivity switching of the ground fault relay in each direction according to the embodiment of the present invention.

FIG. 4 is a distribution line protection circuit diagram using a conventional slight ground fault relay.

FIG. 5 is a vector diagram showing zero-sequence voltage and current.

[Explanation of symbols]

1... Bus line 2a to 2f...Power lines CBa~CBf...Distribution line breaker CTa~CTf...Current transformer PT...Voltage transformer GPT…Ground voltage detection transformer VG…Slight ground fault relay 10... Directional ground fault relay device 11, 12...A/D converter 13, 14, 16, 17... Arithmetic unit 15...Storage section 18...Zero-sequence voltage determination section 22...Sensitivity switching section 23...Ground fault line determination unit.

Claims (1)

[Claims] [Claim 1] When the system is healthy, the three-phase voltage of the bus bar and the three-phase current of each distribution line are detected, the zero-sequence voltage of the system and the zero-sequence current of each distribution line are calculated, and this zero-sequence voltage and each zero-sequence voltage are calculated. The vector differences in the phase currents before and after the accident are calculated and used as inputs for the directional ground fault relays of each distribution line, and the sensitivity of each directional ground fault relay is switched to high sensitivity and returned to normal sensitivity if it does not operate. A method for detecting a slight ground fault fault line in a high-voltage power distribution line, characterized in that sensitivity switching is performed sequentially until one of the relays is activated, and a distribution line in which a slight ground fault has occurred is selectively cut off.