Mr

[johnnyvuus]

I just want to know how to select the primary and secondary of the 3 phase transfomer being Delta or wye?

 

[augie47]

may get corrected, but I can't think of any condition where the primary would be wye. Might be fed from a wye system, but X0 would not be used.
The secondary would depend on your needs, Wye or Delta.
(480vs 480/Y277; 240 delta; 480 delta; 208Y/120, etc)

 

[barbeer]

I would think that issue is a design choice, certain equipment could need the full 240 in lieu of 208 I guess.

 

[LarryFine]

Johnny, tell us about the intended loads' requirements.

 

[jtester]

Wye connections on the high side are common in higher voltages, 25 kv and 34.5 kv for example, they are less expensive, and a little more forgiving when subjected to high voltages. Wye connections are also more common in underground high voltage systems because they aren't susceptable to ferroresonance.

Jim T

 

[LarryFine]

Wye connections on the high side are common in higher voltages, 25 kv and 34.5 kv for example, they are less expensive, and a little more forgiving when subjected to high voltages. Wye connections are also more common in underground high voltage systems because they aren't susceptable to ferroresonance.

No argument there, but a transformer with a wye primary should have the neutral point left floating. Don't bond it or connect it to the source neutral or anything else.

 

[jtester]

No argument there, but a transformer with a wye primary should have the neutral point left floating. Don't bond it or connect it to the source neutral or anything else.

Larry

I'm not sure I agree, my GE Distribution Transformer Manual says that wye-wye should only be used on 4 wire primary systems, and then only if the system neutral and the transformer primary neutral are tied together, if not excessive voltages will develop.

I completely agree on wye-delta transformer banks with 3 transformers, but on others, the primary neutral should be solidly tied to the system neutral.

Jim

 

[LarryFine]

Yes, wye-wye is different. It's basically three 1-phase transformers sharing a common conductor. It's the wye-Delta I was speaking about.