208v to 480v transformer 2

[grandprix5573]

Recently we have been looking at a new piece of machinery. The power requiremnts for this is 3ph 460v @ 100A. Currently we have 3ph 208V service. We have been told that a 112.5KVA step-up transformer will give us what we need. With a set-up like this, what would be the required amperage service coming in at 208 need to be in order for this to work? Or is it not important? From the little i know about this kind of stuff (and i may be wrong) the amperage i need coming in at 208V is relevant to the amount i want to boost the voltage (480V). I have an electrician coming in to take a look but i always like to get a second, third, or fouth opinion

 

[dpc]

It will be (480/208) times the required 480 V current or about 230 A. If this involves starting a large motor, someone will need to look at the voltage drop during motor starting as well.

David Castor

http://www.cvoes.com

 

[davidbeach]

And, very importantly, make sure you get a 208 delta - 480 wye transformer not the far more common 480 delta - 208 wye transformer.

 

[dpc]

Yes, that's a good point.

 

[edison123]

Is this new machinery having only motors ? If yes, then it will be far cheaper to rewind them for 208 V.

Muthu

http://www.edison.co.in

 

[grandprix5573]

We hit a bit of a road block on this one. The current power coming into our building is only a 208V 100A service. So, were now looking into a possible 480V drop from the pole. I just need to build this budget before moving on a machine. To bad National Grid is the worst for getting any type of help if your not an electrician or engineer.

 

[dpc]

If this equipment actually be new, I'd ask the manufacturer if they would provide a package designed for 208 V service. You would still have increase the capacity of your service, but staying at 208 V might be less expensive.

If you take a new service at 480 V, you could install your own transformer to convert the incoming 480 V to 208 V to serve the rest of the facility.

If you are thinking about a 480 V service plus a separate 208 V service, you'll want to run this by your local inspector. The general rule in the NEC permits only one service per facility, but there are exceptions that might apply in your case. The decision is up to your local inspector.

 

[multis6]

Davidbeach, what is the reason and concern for using the 208delta 480wye transformer not the common 480 delta 208wye? I have a feeling that I’m not the only one that has made this mistake.

 

[dpc]

Because the 480V system should be grounded wye rather than ungrounded delta. Normally a 480-208 transformer is used as a stepdown transformer so the 208V winding needs to be grounded wye. It's just the opposite here since this is a step-up.

 

[multis6]

Yes of coarse…. Thanks for the refresher

 

[jfpe]

Davidbeach,

What are you thoughts on an autotransformer for this application?

I assume it wouldn't work based on the 100A service, but I'd like to hear you thoughts in general.

I know an autotransformer would be smaller, lighter, cheaper, and more efficient. Is there a reason it wouldn't work?

-John

 

[davidbeach]

If you can find one, and one without a delta tertiary, I don't see why not. But that's not an animal I've ever run across.

 

[waross]

I have done quite a bit of voltage adjustment with standard transformers re-connected as auto-transformers. I have used 480:120 Volt transformers as auto-transformers to convert from 480 Volts to 600 Volts and from 600 Volts to 480 Volts. In one plant we were going from 600 Volts to 480 Volts and back to 600 Volts (don't ask) with standard 480:120 Volt transformers.
I can't think of any standard voltages that may be reconnected to boost 208 volts to 460 Volts or 480 Volts (standard supply voltage for 460 Volt equipment.)

But Hammond may make a suitable auto-transformer.
Look at a Hammond #Y112QTC

http://hammondpowersolutions.com/upload_files/htp-10_sec9.pdf

Disclaimer; I spent some time on the Hammond site. I would want a Hammond rep to reassure me that this transformer will accept 208 volts in for 460 or 480 Volts out.


Bill
--------------------
"Why not the best?"
Jimmy Carter

 

[jfpe]

Here is wiring diagram SCD 14 for the Hammond Y112QTC. There are a lot of taps, since the possible voltage are 208Y,240Y,400Y,480Y, and 600Y.

I assume 208Y:480Y requires taps X1,X2,X3/H4,H5,H6.

-John