Wye/ Wye transformer/ distrobution bus problems
Wye/ Wye transformer/ distrobution bus problems
(OP)
We have 6 oil filled ground mounted transformers at my facility. All are locked type, ground mounted transformers with primary and secondary feed below ground. Primary feed(power company side) 12470VAC, capacitor bank (PF correction network), then 12470 to 480 (in plant distrobution). Five of these units are delta-wye, one of them is wye-wye.
The wye-wye unit feeds a bus distribution system and we are experiencing failures at the bus, some of them catastrophic with the bus plug being physically being blown off the bus by the arc. It is only on the wye-wye rail. Any suggestions what could be causing these failures.
The wye-wye unit feeds a bus distribution system and we are experiencing failures at the bus, some of them catastrophic with the bus plug being physically being blown off the bus by the arc. It is only on the wye-wye rail. Any suggestions what could be causing these failures.






RE: Wye/ Wye transformer/ distrobution bus problems
Can you provide any more information on the bus plugs? Can you provide more detail on what happens when they 'blow off' of the busway? Is there anything going on in the plant at the time?
If the bus plugs are being blown off, there is either something wrong with the way they are installed or for some reason there is a short circuit flowing through the bus plug that exceeds it's short circuit withstand rating.
There will be a phase angle difference between they wye-wye transformer and the delta-wye. That shouldn't be a problem if there is no interconnection between their secondaries. Is your system somehow paralleling the output of the wye-wye transformer with one of the others (through a bus plug??).
RE: Wye/ Wye transformer/ distrobution bus problems
If you aren't trying to parallel the systems, I'd guess that the failures don't have anything to do with the fact that the transformer is wye-wye. I expect that faults on the bus are caused by insulation failure or something getting into the bus. If there is higher arc energy, it is because the protection is different, resulting in longer clearing times, or the transformer impedances are lower causing higher fault currents.
RE: Wye/ Wye transformer/ distrobution bus problems
None of the transformers secondaries are connected in parallel, that was the first thing that I thought but I can't find anything that shares a connection. A lot of our equipment has come from Canada and have 480 to 600 transformers at the machines and I am looking to see if somehow this voltage is making it back to the bus somehow but doesn't appear likely. Also I would expect this to occur at the same machine or machines if it was related to one of these step up transformers.
One of the delta transformers shares a primary feed with the wye. Not sure what this could mean if anything.
RE: Wye/ Wye transformer/ distrobution bus problems
RE: Wye/ Wye transformer/ distrobution bus problems
Pretty sure the boxes are connected well. While I can't speak for everyone, I know the quality of work that most of the techs perform.
RE: Wye/ Wye transformer/ distrobution bus problems
Have you verified that the transformer neutral is properly grounded?
RE: Wye/ Wye transformer/ distrobution bus problems