Transformer questions

[jobokrma]

We have one building that has 208V Wye system in it and i need to install a transformer for a 480V Delta to run an air compressor. We have the compressor already and my boss wants to use that in this building.
Can we just buy a 480V delta to 208V Wye transformer and and hook it up line side to the 208 wye and get the 480 delta we need? Or is there a different transformer for this?

My load will be 60 amps @ 480V so i think i need a 75KVA transformer what will my line side breaker need to be and wire size for line side:?.

Thank you for looking at this

 

[electrofelon]

We have one building that has 208V Wye system in it and i need to install a transformer for a 480V Delta to run an air compressor. We have the compressor already and my boss wants to use that in this building.
Can we just buy a 480V delta to 208V Wye transformer and and hook it up line side to the 208 wye and get the 480 delta we need? Or is there a different transformer for this?

My load will be 60 amps @ 480V so i think i need a 75KVA transformer what will my line side breaker need to be and wire size for line side:?.

Thank you for looking at this

Best to get the correct transformer which would be 208 delta to 480y/277 wye. Using a 480 delta means you need ground detectors and it's generally just simpler, easier, and less liklihood of having equipment voltage rating issues to make it grounded wye - e en if you don't need a neutral. If you use a 480 delta to 208 wye in reverse, DO NOT bond or land the 208 neutral on the wye point, leave it floating.

 

[7635tools]

I’d check the compressor to make sure you can’t change the motor taps to make it 208. A lot of 3 phase motors are dual voltage. You would also have to change the overloads on the starter and jumpers on the control transformer if it has one.


Sent from my iPhone using Tapatalk

 

[Frank DuVal]

Yes, first check the motor nameplate, as most all general purpose compressor motors are dual voltage.

And also yes to a 208 delta to 480/277 Y secondary to make grounding easier (ok, logical....).

 

[Jraef]

I don't think it matters if the 208V side is Delta or Wye, but if it is Wye, do NOT ground the Wye point on that side.

But as to the 480V side, Wye is definitely better for the reasons stated, albeit not likely on the shelf. If you are forced to use a Delta winding on the 480V side, you can ground one leg and make it a Corner Grounded Delta, which then has other rules to follow and, I dare say, add some decent signage to let any future electricians know what you did.

If there is a VFD on the compressor however, do NOT use Delta of any kind, wait and get the 480/277V transformer and ground the X0 terminal. You don't need to run all 4 wires to the machine, but any power electronics are not going to survive well in a Delta system.

As to the size of the transformer, if you are wanting to start it Across-the-Line, 60A means it's likely a 50HP motor and 75kVA is going to mean a WICKED voltage drop on starting which may become a problem for your motor. I would not recommend smaller than a 150kVA for X-Line starting of a 50HP motor. If you have a Wye-Delta starter or Soft Starter on it, you can get away with a 115.5kVA, but the only way to get away with a 75kVA will be if it has a VFD on it.