Voltage problems and 13,200-480V transformer failure

[Nigel Chivers]

My plant has a rented 13,200-480v 2000kva transformer due to the original failing early November 2008. That day we also lost many power supplies, VFD's and much more.

Now this week we have varying 3 phase from 39-550 volts, where normally it should be 480 volts. We have other problems such as ups's beeping and equipment failing.

Our local utility department are at a loss as to what could be causing the problems. Any advice is appreciated. Thanks, Nigel.

 

[mxslick]

Check the 480 volt side switchgear and bus/cables from the transformer. Sounds like a loose or floating neutral situation.

I presume this is not an ungrounded delta system?

Did the utility double-check the primary fuses, cutouts or breakers? Any arcing or bad connections there may also cause these problems.

And why did the original transformer fail?

 

[ZElectric]

Voltage Problem

Voltage Problem

I also would look at the grounding. To assure you have a good ground a ground tester can be used. Just attaching the transformer to a ground rod doesn't always cut it. A grounding grid may have to be installed. Is the soil sandy in that area? Another thing you might want to do is put a monitor on all three phases and record for a week now and after you establish a good ground. I've seen as one phase goes up in voltage the others lower. If you plot it on a graph the ground seems to move.

 

[brian john]

I also would look at the grounding. To assure you have a good ground a ground tester can be used. Just attaching the transformer to a ground rod doesn't always cut it. A grounding grid may have to be installed. Is the soil sandy in that area? Another thing you might want to do is put a monitor on all three phases and record for a week now and after you establish a good ground. I've seen as one phase goes up in voltage the others lower. If you plot it on a graph the ground seems to move.

While grounding is important, the above post will buy you nothing to check a transformer with voltage issues.

is the transformer 480/277 wye Solidly grounded, HRG or ungrounded or 480 delta.


1. Does the transformer have automatic tap changer?
2. During a schedule check all connections,
3. TTR the transformer.
4. Monitor the voltage on the secondary
5. Check all bond/ground connections.

And do this quick

 

[Pierre C Belarge]

There is some very good info presented, I just want to add one more item.

I am shooting in the dark, as there was not much info presented by the OP as to the nature of the failure.

When the transformer failed, did it damage the conductors on the loadside?
Did anyone megger those conductors?
I would check the neutral termination/grounding, and the integrity of the conductors on the secondary side of the transformer.

 

[stormywyo]

It certainly sounds like a classic loss of the neutral somewhere between the transformer and the service gear.. Could be a loose or corroded connection. Does the 13.8kv transformer feed another customer?? It could be on their side.