Transformer wiring

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karn

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Electrician
Someone wired a 75kva 480v 3phase to 208v transformer backwards (line side on load side), when I flipped the disconnect the transformers breaker tripped, the main for that panel did not trip, but the big main switch outside opened up and will not reset, and it reopens every time I try to close it? Any idea what happened?
 
Was it intentionally wired in reverse, i.e. as a step-up transformer... or wired in reverse as in a major blunder?
 
Reversed as in H1 H 2 and H3 was landed on the x1 x2 x3 lugs, it wasn't intentional, he was not aware of the correct wiring
 
So you have 480 volts on the low voltage side and 1100+ volts on the high side?
 
Connecting the supply power to the nominal secondary winding of a typical power transformer can far more than double the peak inrush current for the first cycle. That could be causing an instantaneous trip of an overly sensitive or damaged main breaker.
 
karn said:
Someone wired a 75kva 480v 3phase to 208v transformer backwards (line side on load side), when I flipped the disconnect the transformers breaker tripped, the main for that panel did not trip, but the big main switch outside opened up and will not reset, and it reopens every time I try to close it? Any idea what happened?
Click to expand...

karn -
Yeah, a few. However, first:
What exactly is the "big main switch"? Bolted pressure switch? Circuit Breaker? If CB, molded case? Fixed TM trip? Electronic trip?

ice
 
GD -
Do you have any references on the 2X inrush? Self gathered data would be good - as in you have seen it, measured it.

Reason I'm asking is:
With the voltage at 2.3X rated, I'm thinking the core is more than majorly saturated. The winding is going to look like a dead short. Current is limited by the winding DC resistance and the feeder reactance. Just guessing
 
karn said:
... the big main switch outside opened up and will not reset, and it reopens every time I try to close it ...
Click to expand...

Big Donkey-like Safety issue: I would not recommend attempting reclosing more than once - really - don't. It may be tripping because the system (read conductors) is damaged and you are closing into a dead short. Not good. OSHA even tell you not to do this.

Highly recommend: Before you attempt another reclose, get your megger and check the conductors phase to phase and phase to ground.

I'll let you translate "Big Donkey-like"

ice
 
Ok so we found a loose ground wire on the ground fault interpreter in the main switch (bolted pressure switch) also the safety lever for the fuse door was broken off, we are guessing this is why it would not reset,, now I wonder if the transformer is any good
 
iceworm said:
Big Donkey-like Safety issue: I would not recommend attempting reclosing more than once - really - don't. It may be tripping because the system (read conductors) is damaged and you are closing into a dead short. Not good. OSHA even tell you not to do this.

Highly recommend: Before you attempt another reclose, get your megger and check the conductors phase to phase and phase to ground.

I'll let you translate "Big Donkey-like"

ice
Click to expand...


There's a transfer switch that we had turned off so there's no load, we tried 3 times
 
Somehow when the switch opened it broke off the safety lever OR the safety lever was broken off after the switch was already closed, this is the reason it would not reset to a closed position, as for the transformer it seems to work fine with the correct wiring now
 
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