Backfeeding Padmount to Feed Utility?

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JoeTroubleShoot

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I should say first that I work for a POCO that is attempting emergency load relief. They are attempting to backfeed a 4kv wye 4 wire circuit with a generator and a 277/480v delta/wye padmount. This will be feeding maybe 30 single phase wye transformers, maybe two or three phase wye banks, and a few delta connected pad mounts. Not %100 on the details, but that's the rough scenario.

It seems like a bad idea to me, but is it safe for the customers load? If so, how should it be connected on the secondary and primary side? If 277/480, should the neutral be floated on the primary(277/480) and/ or should one phase on the secondary(4kv) side be grounded?

I will not be connecting this or giving any information to the engineers that came up with it, so there's no danger of your information being put to use. I had a bad feeling about the idea and I don't have an engineering degree so I'm looking for some info. Also, sorry if this should be in another section.
 
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GoldDigger

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JoeTroubleShoot said:
I should say first that I work for a POCO that is attempting emergency load relief. They are attempting to backfeed a 4kv wye 4 wire circuit with a generator and a 277/480v delta/wye padmount. This will be feeding maybe 30 single phase wye transformers, maybe two or three phase wye banks, and a few delta connected pad mounts. Not %100 on the details, but that's the rough scenario.

It seems like a bad idea to me, but is it safe for the customers load? If so, how should it be connected on the secondary and primary side? If 277/480, should the neutral be floated on the primary(277/480) and/ or should one phase on the secondary(4kv) side be grounded?

I will not be connecting this or giving any information to the engineers that came up with it, so there's no danger of your information being put to use. I had a bad feeling about the idea and I don't have an engineering degree so I'm looking for some info. Also, sorry if this should be in another section.
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Since the normal service HV is wye, then the output side of the backfed transformer must also be wye, and the neutral point should be grounded. But whether it is or not should not affect customers as long as an adequate neutral conductor is part of the distribution system. (And 4-wire suggests that.)
Whether the input side (480Y/277) of the transformer should be grounded and where and what voltages should be used depends on how the generator needs to be loaded. It also will not have any direct effect on customers.
The backfed transformer should not be expected to handle its full rated power when used in reverse. And the voltage ratio under load may not be exactly the same as the voltage ratio under load when working in the forward direction.

As long as they have a competent EE doing the design it should be OK.
 
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JoeTroubleShoot

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MA
Thanks for the quick response. I had bad info and thought they were trying to backfeed with a normal delta/wye pad mount.

They are using a specialy made wye/delta 4kv/480vpad mount which I understand. All is up and running now until the heat wave is over. I have faith in the engineers, but some times people come up with things that don't work when they're thinking on their feet.

Had a couple issues in the past that I wasn't involved in where they tried to back feed a d/d on a wye primary circuit and it went badly.
 
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