Vacuum Circuit Breaker

Please download and study this document : ect198.pdf

Excellent site.

But I still don't trust vacuum after the failure of a 11KV 1200A unit. It was only switching 300A but welded closed on 2 phases.

Did the vacuum fail or did the mechanism fail to keep the contacts open ?

i have a (probably unjustified) feeling that if some linkage fails in a VCB, the contact closes due to external air pressure, as against other switchgear which fail safe...

The vacuum failed. It didn't do the motor much good either. One the electricians had to trip the plant incoming breaker. The power company phoned up to fined out what the hell was going on. The PLC that controlled the plant sent a signal on start up and shut down to warn them, tripping the main breaker took them by surprise. Each section of the plant would use 10MW, that just vanishing with out warning, it didn't go down to well

Don't they have vacuum integrity monitors on these? Seems elementary. If the vacuum fails, i can thinlk of many ways to make the CB/Contactor inoperable. Surprising that you had this issue.

Anyway, not my primary area. Still, i would think it was an elementary design feature.

Pity you had this problem. What did the manufacturer say ?

It's not my problem now, I'm retired.

There was no vacuum monitoring on any breaker, common sense says there should have been. But economics get in the way of engineering sense.

It did have one benefit, regular testing of VCB's which probably cost more than the monitoring had it been installed.

I used to hate writing the switching procedures for these, I knew the fault rating of the 440V boards wasn't high enough for parallel operation, all be it for a matter of seconds while the bus-section was closed and one of the feeders opened.

Thanks 4 the reference

Check this out. http://www.joslynhivoltage.com/catVBU.htm