Grounding a 3 Phase 480V Transformer

You're suspicion has high probability of being correct. What is the connection of your transformer and how is it grounded?

http://transmissiondesignhub.blogspot.com

Thank you for you input, I am in a remote spot in Asia and my email is not what I would like it to be sorry for the delay in responding.

The transform is Delta Delta, and the only ground is at the frame there is no neutral.

Grounding conductor is to be connected at the star point of the transformer winding, Neutral cable termination is also precisely at the same spot.

If you measure at No-load there will be insignificant current flow in neutral.

Start switching On the load circuit breakers one by one and keep checking the flow of current in Neutral. Pin point the defective feeders causing flow in neutral.

I guess single phase loads such as lights are not equally distributed on phases.

Please describe the primary side of this transformer and what if any interconnections exist between the two separetly derived systems. This almost sounds like the neutral at the MCC is tied to ground, which it should not be. What is it that should trip that is not?

To clarify:

The system should have only one point where the Neutral is connected to Ground. Any other inadvertent tie points will result in Ground Loops.

The transformer is a Delta, Delta, there is no neutral, the ground is tied to the frame of the transformer. Having said that I have found multiple ground loops. The MCC feeds a lighting transformer, that then in turn has the neutral and ground bonded at the panel. I suspect that there are swapped neutrals and grounds in the field wiring.

Thanks for the help.

Check the Transformer 480Volt connection side if neutral is solidly grounded or not.

If neutral configuration demands solidly grounded then the neutral grounding is improper.

For oil rigs I think neutral is impedance grounded .

There are systems in 480volt whetre neutral is not solidly grounded this case NGR/NGT is applied.

In such cases you will get only 3phase loading,for single phase loading is not possible with this system.

There must be some spurious single phase loading existing and this is causing current in the ground cable .

For single phase loading you should have 480/277 transformer neutral ungrounded.

For Three phase overcurrent protection the connection is same as three phase overcurrent residually connection the only thing the 50/51N earthfault relay is not applied in the residual path.

For earth Fault you should have a CBCT and very sensitive earthfault relay

The CT neutral has to be grounded at one end nearest to the relay.

HOPE THIS SETTLES YOUR QUERRY.

For your reference, you may find Larry Bush's ebook with practicle knowledge on generators of help.

Also the Industrial Electrical course, sample video below...

http://www.youtube.com/v/QNdMrPQMb1E

I was incorrect in stating that the transformer was WYE configured on the secondary, it is actually a Delta, Delta, transformer and there is no neutral connection. The ground is only on the frame of the transformer. Having said that I get roughly 270vac to ground. I am not sure what I should be seeing to ground any assistance here would be appreciated.

There are multiple ground loops and as much as 35 amps on one jumper between the ground bus between MCC'S, there are 2. My suspicion is that possibly neutrals and grounds have been swapped in the field from the lighting panel. I guess that it might be possible to induce the current in the cable if it were placed in a wire way beside 480vac motor power if the run were long enough.

I am also able to see as much as 300 HZ when checking the frequency without using a low pass filter.

Thanks again