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Catastrophic failure SF6 Circuit Breaker

  1. Jan 13, 2009 #1
    We have had a catastrophic failure of an SF6 circuit breaker. This breaker
    was used as a synchronising breaker for a CHP on our 11kV system.
    Does anyone have or can point me to articles on failures (causes & effects)
    of SF6 circuit breakers.

  2. jcsd
  3. Jan 13, 2009 #2


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    I tried to do a little internet searching but all I could really find pointed to installation problems being the cause of most failures. In paticular; connectors and connections.

    I'm sure there are others here that might be able to help.
  4. Jan 13, 2009 #3
    Not an installation problem, circuit breaker has been in operation for a few years. We are focusing on the following as the cause:
    1. Synchronising problem
    2. Excessive number of operations, 2439 ops.
    3. Loss of SF6 gas.
    The extent of destruction of the CB has taken everyone by surprise, including manufacturers and insurance investigators, so one of thr questions is why did the switchgear fail so destructively. The CB was used well within its rating. Had anyone been in the sub station at time, it may well have been a fatality. If I get time later today, I will post some photos.
  5. Jan 14, 2009 #4


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    Try sending a PM to m.s.j -- most of his posts here in the EE forum are puzzles about failure of high voltage power distribution systems. He seems pretty knowledgable about these kinds of questions.
  6. Jan 14, 2009 #5


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    When I was reading about these, there were a couple mentions about maintenance programs where they checked the SF6 gas and contacts. Do you have a maintenance program for your breakers? I'm thinking any documentation might come in handy during insurance investigations etc.
  7. Jan 14, 2009 #6
    We do have a maintenance program and the CB was maintained recently onsite, which is basically a service of external components. However, there is a recommendation (that we didn't know about as it is not stated in the O&M manual), that the CB is serviced at factory after 2000 ops. This had not been done because we didn't know about it. This was a verbal recommendation given by the manufacturer when he carried out the site service.
  8. Jan 16, 2009 #7
  9. Jan 16, 2009 #8


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    Wow. Thanks for sharing BIGEYE. Glad I wasn't in there when it blew. Looks like there was a fairly large fireball involved.

    Let us know if you ever determine what exactly happened.

  10. Dec 16, 2009 #9
    Hope you have now found the problem But your installation has many safety issues. Gen pirpose breakers used for sync duty are rated only at 25% Isc for out of phase switching. What is the ratio of actual FLC and breaker rating. Is your switchgear ventilated. Are you familiar with the hazards of handling decomposed SF6 arc products. Is yours a definite purpose gen breaker? You should be doing mtce, contact res, gas analysis more frequently. Your switchgear should be arc resistant type C or BC to IEEE C 37.20.7. Was this a failure to interrupt fault/load current or a failure to synchronize(close ) A vacuum MV CB will be more robust , ie. higher mechanical life , for this duty but it must have adequate open gap 60hz withstand and have an adequate O-o-P SC interrupting rating
    Hope this helps avoid future problems
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