vacuum circuit breaker foreign material

[jpankask]

Has anyone observed this condition before? We have Siemens vacuum circuit breakers (4160 V and 13800V) but this might not be limited to just these.

When removing from service for a PM, we found some foreign material encircling several of the stabs. The material was black and looked like metal shavings (although not magnetic) and was distributed around the stabs in a concentric circle (almost like it was blown down).

The stabs are coated with a silver alloy and the insulators are made of a proprietary material (so not sure of the exact makeup) that is ceramic like but not completely ceramic. Analysis of the material shows it contains silver, silicon, aluminum, calcium, copper and magnesium with traces of iron, sodium and zinc.

We are ready to cut our monetary losses since supplier is saying it's not their fault but for some extra cash, they will look into it more. I would like to determine some kind of apparent cause to determine if we might experience this again the future. Any experiences or ideas are greatly appreciated!

 

[dpmac]

Is the material on the cell mounted primary "stab" or the breaker mounted "finger"? Any chance we could see a picture?

 

[jpankask]

The black material is located on 4 out of the 6 primary stabs, which come out of the top of the breaker, in our application. The stabs are about 3-4 inches in diameter, extend 12 inches above the top of the breaker and are enclosed in the insulator material except for the top 2 inches. This top part is where the black material is found, all around the stab directly above the insulator material. Laying on top of the breaker all around the affected stabs/insulator is a gray dust material, which I believe is how the black material started out (both have nearly identical chemical composition). I do have pictures but no website to post them on and eng-tips does not like us to post email addresses.

 

[bacon4life]

See this FAQ for posting images:

http://www.eng-tips.com/faqs.cfm?fid=1100

 

[jraef]

H²S in the atmosphere does some funny things to silver plating on bus and contacts. We had some discussions on it in this forum last year, and some of the posters put up some excellent pictures. I'll see if they are still around.

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[jraef]

Here is the paper I was thinking of. Excellent photos at the end.

http://nepp.nasa.gov/whisker/refere...ovsky2002-paper-silver-corrosion-whiskers.pdf

"Our virtues and our failings are inseparable, like force and matter. When they separate, man is no more." Nikola Tesla
Read the Eng-Tips Site Policies at faq731-376
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