VCB Failure

Hi,

Usually, for voltage ranges 1kV- 11kV, they prefer VCB bcoz, for that voltage ranges, it acts as a good interrupting device. Moreover, failure in CB happens mostly bcoz of the mechanical problem(as in your case) and VCB bottle failures are less. You can check the VCB bottles healthiness by conducting hipot tests on periodical basis.

You do one think ... VACCUM Integrity Test ...Keep open CB BKR and appy accross between opened Vcb bottel around 2.25 time rated voltage in ONE munit if in your Vcb bottel ok it will not break voltage ....in case if any failure test voltage will break ..it means VCB Bottel will failed .....VCB bottel failuer case very rerely...you try this test in praticely i don it ..

Yes, loss of vacuum is the most likely cause of the failure. It requires regular testing, something most people never bother with.

Actually, vacuum circuit breakers have quite high reliability, given (as jraef said) that they get periodic maintenance and testing. I have seen only a couple of vacuum bottle failures during almost 20 years of doing VCB testing for various customers, with a variety of breaker manufacturers. It's more common to see some other mechanical failure that may either damage the vac bottle or cause the contacts not to open or close properly. That's where the maintenance comes in.

I'd much rather have vacuum breakers in medium voltage switchgear then air or SF6 breakers. Some of the new designs like ABB's R-Mag breaker have reduced the number of moving parts in the operating mechanism substantially, so you have fewer possible points of failure and less to maintain (although they still need to be maintained and tested on a regular basis).

Sorry, I didn't mean to imply that vacuum loss was a common occurrence. In fact it's quite the contrary, I have found Vacuum bottles to be very reliable. But the few I have seen fail have all been from loss of vacuum.

Thanks lads, as I said it was purely out of interest. Partly because I worked on the plant about 10 years ago. The only problems I had with the large motors were the slip rings. I had to hand grind them, not a fun job!