Is it technically possible to Loop Feed 2MVA Wye-Wye to 1MVA Delta-Wye Transformer? Fed from 3 Wire, 34KV line from utility distribution line.

[kristian0906]

Currently, we have an existing operation establishment, supplied from a 2MVA Wye-wye transformer. We currently having a power deficiency, we need to have an additional of 1 MVA transformer.

From my experience, it is recommended if we will be having a Delta-wye Type of Transformer instead of a Wye-wye, due to an advantage of separating the system from primary line (utility) to our system. However, the existing transformer that we are currently using is Wye-wye. Can I loop feed the two equipment from a same distribution line?

 

[Elect117]

Equipment on the primary side of the transformer or the secondary side? What kind of equipment?

What do you mean by loop feed?

 

[jim dungar]

Our POCOs are almost exclusively Wye distribution. They have regularly allowed Delta connections, however I don't know if I can can say any of them were loop feed at the transformer terminals.

I would not it to be a problem, as the Wye underground cable neutrals are bonded together and then to a ground rod anyway.

 

[ron]

Shouldn't be a problem if you can add the loop switches and needed protection (the transformer protection will be smaller than the overall loop). The neutral for the existing transformer primary can be carried through the loop, but it will not be brought down to the new transformer because it is a delta primary.

 

[electrofelon]

. The neutral for the existing transformer primary can be carried through the loop, but it will not be brought down to the new transformer because it is a delta primary.

View attachment 2572420

Is there any reason to, or not to, land the neutral on the transformer case as a bonding conductor? I suspect it would be required by the NEC, but I haven't refreshed myself on 250.184

 

[ron]

Is there any reason to, or not to, land the neutral on the transformer case as a bonding conductor? I suspect it would be required by the NEC, but I haven't refreshed myself on 250.184

If these are loop feeds, then when power is routed from the alternate path, you would want an intact neutral. These are feeders and the grounded conductor should remain unbonded.

 

[electrofelon]

If these are loop feeds, then when power is routed from the alternate path, you would want an intact neutral. These are feeders and the grounded conductor should remain unbonded.

But if it's an MGN system, the neutral would be used for bonding. If it's a single point neutral system, I'm pretty sure you would need to bring a grounding/bonding conductor.

 

[ron]

But if it's an MGN system, the neutral would be used for bonding. If it's a single point neutral system, I'm pretty sure you would need to bring a grounding/bonding conductor.

I understood these to be feeders with an ungrounded conductor and an EGC, not a utility MGN

 

[electrofelon]

Reread

I understood these to be feeders with an ungrounded conductor and an EGC, not a utility MGN

Rereading things, it is not clear. In fact the thread title mentions three wire distribution so maybe there is no neutral at all. I saw wye-wye transformer and assumed there would be a neutral. Could use clarification on all these things.

 

[electrofelon]

I understood these to be feeders with an ungrounded conductor and an EGC, not a utility MGN

Note it could be a customer owned MGN, the NEC allows this and that's how I would do it.