We have a problem with a 3 phase transformer at the university where I work and we need advice.
Here's the setup
A 37.5kva 3 phase transformer wired backwards with the 208 Y side being fed with a 50 amp 3 pole breaker. There is no connection to the XO 3 phase 208 volt INPUT.
The "secondary" side is a 480 volt delta hookup feeding a disconnect that supplys a AC unit that was surplus.
after the original installation the setup worked. After a power outage the 50 amp main breaker tripped instantly. We megged the transformer and there were no grounds. We swapped out the breaker with a used one and had the same results. I changed out the transformer with another one and we still have the same problem. There is no load on the secondary as we fed a disconnect and it's still open, not an issue. What is the best place to look for a problem? I pulled the conductors out of the primary and secondary and there was no sign of failure.
any suggestions would be greatly appreciated
Thanks
Dave