Toshiba VCB

[sparky1944]

I am looking at a Toshiba VCB that was used as a contactor for a 4160-V motor. There was an arcing fault at the contactor. Does anyone have experience with this type of failure? Especially with a Toshiba VCB?

Thanks

 

[jraef]

On the outside of the contactor or did you cut open a bottle and see that it had flashed over? If on the outside, arcing to what, phase-to-phase, phase to ground, phase to another device? Was there some kind of fault first and now you are reading conductivity to ground?

I have used a lot of Toshiba vacuum contactors on 4160V and beyond. I have never had an arcing problem. Arcing faults in MV gear can happen from a lot of things, but IMHO if there were a design problem in the contactor, it would be immediately evident to someone like Toshiba who sells thousands of them every month.

I have had moisture problems in MV cabinets that allowed tracking from the terminations to the back panel, which once it happens, is very difficult to correct without rebuilding your isolation system. But that isn't really a problem with the contactor design.

I have also had GE vacuum contactors that failed to ground during UL testing because GE had reduced clearances in their LimitAmp gear at some point and apparently never retested with UL. But that was not technically a contactor design problem either and was easily solved.

I've had a flash-over in Joslyn gear from the contactor terminals too, but that was after a voltage event that cause some MOVs in the same cabinet to vaporize, which provided a flash-over path through the ionized atmosphere in the cabinet. Again, not a design problem with the contactor.

Describe your event in more detail.

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[sparky1944]

I really don't have a lot of information right now other than an event. We had an arcing fault that likely coincided with an operation of the VCB being used as a motor contactor. It escallated into a large arcing fault that did a lot of damage. We have not yet had a chance to take the remains apart so I'm not sure the cause lies at the VCB it is just suspicious that it coincided with the opening event.