Step up transformation?

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thaley68

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Is it feasable to step up to 480 volts from a 120/208 volt 3 phase service?
I have an industrial building with a 2000a,480v, 3ph service. We just purchased a smaller building right next door and built a connection between. My 480 volt switchgear has no available space for another disconnect, however the smaller building has a 600a, 120/208v 3ph service. I was wondering if we could transform up to 480v from the 208v service? I have never even thought about doing this in the past, so I thought I would post here to get some ideas!

thanks

Thaley68
 
I am guessing that there are some 480 volt loads in the second building. Yes, you can do what you are suggesting. I would ask a manufacturer's representative about selection of a suitable transformer. You can just take a 480 step down to 120/208 and wire it "backwards." But if there are transformers designed especially for your situation, it would be better to use one of those.

Welcome to the forum.
 
Reading through your question again brings a question to my mind. What do you mean when you say there is a connection between the two buildings? Is it an electrical connection? If the second building has a service of its own, you can't bring power from the first building to the second.
 
As you step up the voltage you are stepping down the current. (total power stays the same if you ignore all the transformer and wire losses.)

So your 600A service is only going to give you about 260 amps at 480. (208/480) * 600 = 260

Steve
 
Step up transformer

Step up transformer

How do you wire a transformer that's meant for primary of 480V to secondary volt 208v and make it a primary 208v and secondary 480v ?
Do you just reverse the wiring?
 
weressl said:
You can purchase 3 phase transformers with 208V/D primary and 480/277V/Y secondary. That would be the right way to do it from scratch.
Click to expand...
Why??

It is only one way. Of course if if you want a neutral connection, it is probably the best way.

But, if you only need 3-wire and don't mind having a corner-grounded system, then a reverse connected transformer is an acceptable method.
 
There are numerous ways to get this job done, but if I were doing this from scratch, and had the lead time to specify what I thought was the ideal transformer for the job, I would go with a 208V delta to 480/277V wye transformer.

To thaley68: search this forum for threads about reverse connecting transformers, and you will see that it can be done but that there are significant issues to deal with. Depending upon your specific situation, these may be worth dealing with. For example, if you already have a suitably sized 480V delta to 208/120V wye transformer sitting on site, then dealing with the headache of reverse wiring might be worth it.

-Jon
 
LarryFine said:
Yes, but with one caveat: do not connect the neutral of a wye now-primary to the supply neutral; let it float. In other words, wire it as if it were a Delta.
Click to expand...

EATON:
Can transformers be reverse-connected
(reverse-fed)?​
Yes, with limitations. Cutler-Hammer single-phase transformers rated 3 kVA and larger can be reverse-connected without any loss of kVA capacity or any adverse effects. Transformers rated 2 kVA and below, because there is a turns ratio compensation on the low voltage winding that adjusts voltage between no load and full load conditions, should not be reverse-fed.
Three-phase transformers with either delta-delta or delta-wye configurations can also be reverse-connected for step-up operation. When reverse feeding a delta-wye connected transformer, there are two important considerations to take into account:
(1) The neutral is not connected, only the three-phase wires of the wye system are connected,
(2) the ground strap between X0 and the enclosure must be removed. Due to high inrush currents that may be created in these applications, it is recommended that you do not reverse-feed transformers rated more than 75 kVA. The preferred solution is to purchase a step up transformer designed specifically for your application.​
 
LarryFine said:
Yes, but with one caveat: do not connect the neutral of a wye now-primary to the supply neutral; let it float. In other words, wire it as if it were a Delta.
Click to expand...

What would happen if you connected this now primary neutral to the supply neutral?

What about if you connected it to a supply EGC?
 
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