JPS59181916A - Intermittent defect detector - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an intermittent fault detection device for detecting faults that occur intermittently in a power system.

Generally, when a ground fault occurs through an insulator such as an underground cable, an intermittent ground fault often occurs due to the arc extinguishing action of the insulator. This phenomenon tends to occur more easily as the fault point current is smaller and as the system voltage is lower, and is more likely to occur in ungrounded systems or high resistance grounded systems.

Therefore, for convenience of explanation, the ground fault relay device will be described below. A conventional device of this type is shown in FIG. In Figure 1, (1) is an AC power supply, (2) is a power system, (3) is a breaker, (4) is a detector that detects the zero-sequence voltage of the power system (2), and (5) is a reverse voltage. This is a time-limited overvoltage relay. In addition, Fig. 2 shows a reverse time-limiting type overvoltage relay (5
) represents the operating characteristics of

Next, the operation will be explained. The overvoltage relay (5) on the platform where the ground fault (I-fault occurred) at point F of the power system (2) receives the zero-sequence voltage via the detector (4) and responds according to the operating characteristics shown in Figure 2. As is well known, the inverse time limit characteristic is that the operating time decreases as the exposure level increases, and the overvoltage relay (5) enters the protection zone when the contact point between the zero-sequence voltage and the operating time reaches the operating range. It detects that a ground fault has occurred and trips the circuit breaker (3).

Therefore, when a ground fault occurs, the inverse time-limited overvoltage relay (5) must last for a sufficient period of time for the zero-sequence voltage to reach the operating range shown in FIG.

Note that when the power system (2) is healthy, the zero-sequence voltage is zero, so the detector (4)' does not output and the overvoltage relay (5) does not respond.

Furthermore, although the above-mentioned overvoltage relay (5) is of the inverse time limit type, in the case of an instantaneous type, the overvoltage relay (5) operates instantaneously depending on the magnitude of the input zero-sequence voltage regardless of the operating time. Depending on the type of power system used to protect against ground faults, a combination of anti-time type and instantaneous type relays may be used.

As mentioned above, anti-time-limited or instantaneous overvoltage relays have been used to detect ground faults in ungrounded systems or high-resistance grounded systems. There was a problem in that it was not possible to secure enough power, and the instantaneous type was prone to malfunction.

In other words, conventional ground fault relay devices lack reliability in detection operation in the case of intermittent ground faults that occur intermittently, and are susceptible to repeated impacts due to intermittent ground faults and abnormal voltage increases on healthy phases. This had drawbacks such as increasing the damage caused by accidents.

This invention was made for the purpose of eliminating the above-mentioned drawback of the conventional technology that lacks operational reliability in the event of intermittent accidents. Intermittent accidents can be accurately detected by comparing the number of times an accident has occurred with a predetermined value. To provide an intermittent accident detection device that can

An embodiment of the present invention will be described below with reference to the drawings. Third
In the figure, (6) is a counter that counts the number of occurrences of zero-sequence voltage detected by the detector (4), (7) is a setting device that presets the number of occurrences of a ground fault, and (8) is a counter ( This is a determination circuit that determines that an intermittent accident has occurred when the output of 6) exceeds the output of the setting device (7). The figure shows an example of application to a conventional power system (Figure 11).

Next, the operation of the demonstration example will be explained. When an intermittent ground fault occurs at point F of the power system (2), an intermittent fault voltage as shown in FIG. 4(a) appears on the detector (4), for example. The counter (6) converts the intermittent fault voltage input via the detector (4) into a rectangular wave as shown in FIG. 4(b),
A counter or the like is used to count the rectangular wave signals generated within a certain period of time after the first counting of the rectangular wave signals, and after the certain period, the count value is returned to zero and a standby state is entered. In other words, the number of occurrences of ground faults is counted over a certain period of time.

Here, if a ground fault with intermittent self-recovery occurs twice in a certain period of time, if it is an intermittent ground fault, the setting device (7) will be set to 2'.
Set in advance.

Therefore, the determination circuit (8) determines whether the output of the counter (6) (in the example, a signal corresponding to ``8'') is a predetermined value set by the setting device (7) (for example, a signal corresponding to ``2''). If it exceeds this, it is detected that it is an intermittent accident and the breaker (3) is tripped. Or issue an alarm and notify the supervisor that there is an intermittent ground fault.

Therefore, the embodiment can detect intermittent ground faults that could not be detected with conventional overvoltage relays (5), preventing damage caused by repeated shocks and abnormal voltages occurring on healthy phases (from spreading). becomes possible.

In addition, although the above-mentioned embodiment shows one used in combination with a conventional relay, it may be used alone, or even if it is built into a conventional relay, the same effect as in the above-mentioned embodiment can be obtained.

In addition, although the above embodiment describes the case where it is applied to a ground fault network modification device, other "@
Needless to say, it may be an electrical device.

As described above, according to the present invention, since the number of occurrences of accidents is compared with a predetermined value, it is possible to obtain an intermittent accident detection device that can accurately detect intermittent accidents.

[Brief explanation of the drawing]

Fig. 1 is a block diagram showing a conventional ground fault relay device, Fig. 2 is an operation characteristic diagram explaining the operation of the relay in Fig. 1,
FIG. 3 is a block diagram showing an embodiment of the intermittent accident detection device according to the present invention, and FIG. 4 is a time chart diagram for explaining the operation of the counter in FIG. 3. In the figure, (4) is a detector, (6) is a counter, and (7
) is a setting device, and (8) is a determination circuit. In addition, in the figures, the same reference numerals indicate the same or equivalent parts. Agent Makoto Kuzuno

Claims (2)

[Claims] (1) A detector that detects the faulty amount of electricity in the power system, a counter that counts the number of times this detector detects the faulty amount of electricity, and an intermittent fault determined if the output of this counter exceeds a predetermined value. An intermittent accident detection device equipped with a judgment circuit. (2) The intermittent accident detection device according to claim 1, wherein the detector detects a zero-sequence voltage.