reasons of flash in air break contactor of 3.3kV motor

[khanengr]

hi dear all,

we had a blast in a 3.3kV air breaker contactor connected to motor of same ratings, the flash blast occured the moment we tried to close the switch, after a period of long time. But first, we opeated the above mentioned contactor, by giving it 3.3kV supply on NO LOAD and it operated fine, but when we connected motor (load), flash occurs, kindly suggest possible reasons thanks.

 

[jraef]

What do you mean by "flash"? Whenever you make contacts in air and a load is connected down stream, you will see a brief flash as the arc jumps the gap when the dielectric properties of the air gap become lower than the potential across the gap. It is even worse when breaking a set of contacts. It's for that reason that many people no longer use air break contactors on medium voltage motor applications, choosing instead to go with vacuum contactr technology. If you don't like the flash, change it out with a vacuum contactor.

But another VERY disturbing aspect of this is that you saw the flash. I hope for your sake it was seen through air vent openings in the enclosure, not because you operated an air break contactor with the door open!

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[rhatcher]

jraef,

You are correct. It is hard to imagine being able to see the normal flash of an air break contactor unless the door is opened and the arc chute is removed. Like you, I hope he wasn't operating the starter like this. That is a recipe for disaster!

The OP did use the words "blast" and "flash" interchangeably. For a "blast", the implication is that there is a fault in the motor feeder cables or in the motor itself. Even in this case, it is hard to imagine being able to see the "flash" that accompanied the "blast" if the door was closed and the arc chutes were installed. That is, of course, unless the door was blown open by the fault.

I don't think we can come to any good conclusion without more information from the OP clarifying whether this was a "flash" or "blast", whether any fuses were blown or overloads tripped, and what damage, if any, resulted to the contactor from this event.