Catastrophic failure SF6 Circuit Breaker

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Discussion Overview

The discussion centers around a catastrophic failure of an SF6 circuit breaker used in a synchronizing role for a combined heat and power (CHP) system on an 11kV electrical network. Participants are exploring potential causes and effects of such failures, sharing experiences, and seeking articles or insights on the topic.

Discussion Character

  • Exploratory
  • Technical explanation
  • Debate/contested

Main Points Raised

  • One participant notes that installation problems are often cited as causes of SF6 circuit breaker failures, particularly issues with connectors and connections.
  • Another participant emphasizes that the breaker had been operational for several years and suggests potential causes including synchronizing problems, excessive operations (2439 ops), and loss of SF6 gas.
  • Concerns are raised about the extent of destruction caused by the failure, with some participants expressing surprise at the severity and noting potential safety risks.
  • A suggestion is made to check maintenance programs, particularly regarding SF6 gas and contact inspections, as documentation could be useful for insurance investigations.
  • It is mentioned that the breaker was maintained recently, but a critical recommendation for servicing after 2000 operations was not followed due to a lack of awareness of this guideline.
  • One participant raises questions about safety issues related to the installation, including the appropriateness of the breaker for synchronizing duties and the need for more frequent maintenance and gas analysis.
  • There is a discussion about the robustness of different types of circuit breakers, with a suggestion that a vacuum MV circuit breaker may be more suitable for the application.

Areas of Agreement / Disagreement

Participants express various viewpoints on the causes of the failure, with no consensus reached. Some focus on installation and maintenance issues, while others highlight operational factors and safety concerns.

Contextual Notes

Participants mention missing recommendations in operation and maintenance manuals, as well as unresolved questions regarding the specific nature of the failure (e.g., whether it was a failure to interrupt fault/load current or a failure to synchronize).

Who May Find This Useful

Individuals involved in electrical engineering, maintenance of high voltage systems, or those interested in failure analysis of circuit breakers may find this discussion relevant.

BIGEYE
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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.

TIA
 
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BIGEYE said:
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.

TIA
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.
 
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.
 
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 knowledgeable about these kinds of questions.
 
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.
 
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.
 
Image links:
http://tinyurl.com/9yvsw3"
http://tinyurl.com/7ou8pa"
http://tinyurl.com/8vqxkj"
http://tinyurl.com/7k85ze"
http://tinyurl.com/7wrvjk"
http://tinyurl.com/7s4v9p"
http://tinyurl.com/7vtvhl"
http://tinyurl.com/7z3yhq"
http://tinyurl.com/7r6g6a"
http://tinyurl.com/8ofrr3"
http://tinyurl.com/84y37h"
http://tinyurl.com/8tewxl"
http://tinyurl.com/92jcwu"
http://tinyurl.com/8ysw6t"
http://tinyurl.com/9aochw"
http://tinyurl.com/7tll6k"
http://tinyurl.com/8tufz4"
http://tinyurl.com/6v3be7"
http://tinyurl.com/7a8zxt"
http://tinyurl.com/92glox"
http://tinyurl.com/9scqhc"
http://tinyurl.com/85xmv6"

Larger pics are available.
 
Last edited by a moderator:
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.

Regards
 
BIGEYE said:
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.

TIA

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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