Ask Me Help Desk - Vacuum circuit breaker

Good day,
We have a vacuum circuit breaker (1200A, 15KV, manufactured by Siemens) which feedd power to 13750HP motor. We had three similar incidents on the same 13.8KV substation on these breakers since it was commissioned on 1994. The last incident occurred on Feb. 1st, 2010 when a technician was trying to rack in the breaker. A flashover occurred imidiately after the breaker passes the test position. The technicain was sure that the breaker was open at that moment. The flashover led only to damaging the breaker phase B& C contacts (welding marks), smoke, bus pitting and damage to the mechanisim located on the switchgear floor where the racking arm is located.
What will cause the flashover to occure if the breaker was open?
Will a defective vacuum chamber cause the flashover?
Will the tripping mechanisim work if the vacuum chamber defective?
Regards,
Sam

Sounds like failed vacuum bottles may be the culprit. Vacuum contacts are only separated by a very small gap when open and rely on the lack of air present to not flash over. The tripping mechanism will still work but the breaker will not be able to isolate the circuit with failed bottles. A vacuum bottle integrity test is recommended as routine maintenance on all VCB's. My shop specializes in repairs and bottle upgrades for all OEM's.

Thanks Zog
We sted the bottles and they passed the test. We also conducted semulation on isolated switchgear and observed 5 out of 15 breakers changed status to closed position when moved from test position (T).

Would you explain to me what happened during the racking-in process? Does the breaker close and then open instantly after the Test position?

Quote:

Originally Posted by smile4shy

thanks Zog
We sted the bottles and they passed the test. we also conducted semulation on isolated switchgear and observed 5 out of 15 breakers changed status to closed position when moved from test position (T).

Would you explain to me what happened during the racking-in process? Does the breaker close and then open instantly after the Test position?

Sounds like you have some serious issues. No breaker should ever change status to close while racking, there are interlocks to prevent racking a closed breaker.

We have seen a few different issues with Siemens GMI breakers, one is a failure of the trip free interlock roller in the cell, we saw one of these at a plant, looked at all the cells and saw nearly 30% of these rollers were damaged. This device is what prevents racking in a closed breaker. Luck for the plant they were remotely racking the breaker when this one occurred and no one, besides our "robot" was injured.

THe other GMI failure we have seen is broken push rods, this allows the indicator on the breaker to say open when the phases with broken push rods are actually closed.

Both of these are coverd briefly at the end of this power point http://www.cbsnuclear.com/downloads/...mitigation.pdf

I can send you more detailed info if you like, you can contact me at Nuclear Safety-Related Servicing of Safety Related Class 1E Circuit Breakers - 10CFR50 Appendix B Qualified - CBS Nuclear Services, Inc. - Scott (Zog)

Quote:

Originally Posted by Zog

Sounds like you have some serious issues. No breaker should ever change status to close while racking, there are interlocks to prevent racking a closed breaker.

We have seen a few different issues with Siemens GMI breakers, one is a failure of the trip free interlock roller in the cell, we saw one of these at a plant, looked at all the cells and saw nearly 30% of these rollers were damaged. This device is what prevents racking in a closed breaker. Luck for the plant they were remotely racking the breaker when this one occured and no one, besides our "robot" was injured.

THe other GMI failure we have seen is broken push rods, this allows the indicator on the breaker to say open when the phases with broken push rods are actually closed.

Both of these are coverd briefly at the end of this power point http://www.cbsnuclear.com/downloads/...mitigation.pdf

I can send you more detailed info if you like, you can contact me at Nuclear Safety-Related Servicing of Safety Related Class 1E Circuit Breakers - 10CFR50 Appendix B Qualified - CBS Nuclear Services, Inc. - Scott (Zog)

When we simulate, the breaker indicator changed between the closed and open with no problems. So I assume, the rod connected to the indicator (Close) is OK.
Secondly we found problems with the racking interlock which prevents the breaker from racking in 'closed' breaker. The technician assured that the breaker was 'Open' and 'Discharged' indicator was clear.
What would change the breaker to 'Close'?
Appreciate your response.

Need 6 vacuum bottles for 3ah22 siemens vcb breakers please email [email protected]
Thanks
Marco

What are the best solutions to prevent flash over in the VCB to prevent damaged on it? I need an urgent answer. Please help me.