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Why does the circuit breaker’s contact jitter?

Some customer once made a record of the wave that the analog circuit-breaker contact jittered for analysis. The relay tripping and reclosing exit are connected with the analog circuit-breaker tripping and reclosing circuit. The contact of analog circuit-breaker is connected with the binary input of relay which gives feedback to the relay and controls the output.

In the below figure, it is a typical waveform to simulate eternal fault. From the figure, it is phase A grounded fault. The waveform from top to below is phase A, B and C voltage, phase A, B, C current. The lowest is the 4-channel binary waveform. The first channel is connected with the phase A analog circuit-breaker’s contact and the fourth channel is connected with the relay’s reclosing exit contact.

The waveform and binary trip are correct from the beginning. The waveform and binary inverse are exactly consistent, but the problem is located in the last accelerated part. After the after-acceleration action tripped secondly, it should keep binary output status until the test ends. But from the wave recording at phase A analog circuit-breaker’s contact there was a slight pulse after accelerated tripping and the related wave jittered. It indicated there was reclosing and tripping in short time after the circuit breaker accelerated tripping

Ponovo circuit

Why is there a pulse? Is there any problem with the circuit breaker? Actually, the three circuit breakers in customers have the same problem. But the three beakers are produced in different period. Our engineers have to find the reason.
The customers directly connected the circuit breaker without operation box. Is it possible that the tripping and reclosing time is too short to jitter? In laboratory, when the circuit breaker with relays simulates the same fault, there is no jitter.

After contacting with customers, our engineers found the fourth binary in the diagram was the contact of reclosing exit. There was a reclosing pulse. But we checked carefully: after the acceleration tripping, the reclosing pulse still existed. The reclosing circuit of the breaker was still on state. By this the breaker will reclose again. Here we couldn’t see the tripping pulse, but we can imagine the tripping pulse didn’t disappear in wrong reclosing tripping. So the tripping circuit of the breaker was still on state. Then the analog beaker tripped again, this was the reason that appeared the slight pulse. After that we could see the pulse inverse end, so there was no the third reclosing.

The reason is not the short time of tripping/ reclosing pulse duration, but long time continuance. If we conclude the reason into the relay’s tripping/ reclosing pulse, the problem can’t be solved. The pulse length is fixed rather than adjustable. It is set for the relay’s reliability.

How to solve the problem? Let us check the binary input reverse situation. The reclosing pulse reversed 40ms; the analog circuit breakers phase A reversed. It is after-accelerated tripping to avoid the relay’s response time. The tripping time of analog breaker is about 20ms. The tripping/ reclosing time of the breaker is the minimum. If we lengthen the tripping/ reclosing time, and reclose the breaker after the reclosing pulse disappears, the breaker will not appear the second wrong reclosing.

This analysis is approved by customers. We lengthen the tripping/ reclosing time of the breaker and make test again, then the jitter disappears.