Vacuume circuit breaker blast?

One possibility is the equipment was not rated for the available short circuit current. That may explain the damage. If the breaker cannot interrupt the short circuit current, it continues to flow until something gives. With such high current levels, that does not take long.

Hi,

It is possible that vaccum of the bottle was lost. Without regular inspection you will not know for sure whether a vaccum bottle is healthy. The bottle may blast even while interrupting normal current or no load transformer switching as the travel is of the order of 6mm for a 11KV bottle. Unlike SF6 so far I have not seen any lock out is provided by any manufacturer for a loss of vaccum bottle.

Regards,

Swagata

Is English you first language? I don't mean to be critical, but it may be worth running your contributions through the spell-checker before submitting in future. It would be difficult to find 'vacuume" if one was searching for the correct word 'vacuum'.

I, too, often make errors like this, that's why I try always to remember to run posts through spellchequer...

Failure of the vacuum bottle may not cause a catastrophic failure or anything except an inability to interrupt the circuit. A vacuum switch manufacturer I worked for performed NEMA prototype testing of a 25 kV, 200 amp switch. During one test we were checking for thremal stability under full load. The switch passed the test. When it was dissassembled, one of the bottles was cracked clear through. (That did not affect the thermal results.) When we looked at the current traces, that pole had not interrupted when the switch was opened at the end of the test. (Since that was not the point of that part of the test, we hadn't noticed it.) This was for a load break switch. There might be different results with a fault interruper.

Having experienced a vacuum interrupter failure "up close and personal" on a 13.8 kV feeder breaker, I don't doubt your description. Our failure analysis indicated the bottle was full of air due to a defect in the bellows weld. When the contacts separated upon opening the breaker, , the arc was not extinguished in that interrupter. All of the contact material was vaporized, and the air in the bottle superheated, greatly increasing the pressure inside. Since the interrupter is designed for higher pressure outside (vacuum inside), it promptly exploded, spreading vaporized copper and superheated air throughout the cubicle.

Even though the cubicle door was closed & latched, the force of the expanding gas bent the door and blew it open, shredding the latch bolts. Fortunately, the door and walls of the cubicle absorbed most of the energy, and no other equipment was damaged.

Based on your description, I suspect your switchgear was not designed to contain arc faults (I write that requirement into all my specifications). That's the difference between replacing re-wiring one cubicle and replacing half a substation.

This comment is with respect to Internal arc specification of the switchgear:

I have 25KA 11KV vacuum switchgear that has internal arc test certificate. The Switchgear rating was for 25KA 3 Sec where as internal arc fault test was done for 25KA .15sec.(special test). Obviously this is less than the relay operating time. My question is whether IEC/code specifies anything regarding the duration of internal arc fault test. Or what is the logic of such a small time specified for the test, if 0.15sec is the specified time.