Back Up Generator Question

[Bdan]

Hello, I need to back up a 400Amp single phase service to a restaurant.
The owners of the restaurant have a 250 kw 600/347V gen-set they want me to use. Question is can I connect a single phase load to a 3 phase gen-set? If so should I use a 3 phase 600-120/208 transformer and connect to two phases and neutral or should I purchase a single phase 600-120/240 volt transformer?

Thanks for any suggestons.

Bdan

 

[charlie b]

Their genset will be imbalanced, no matter what you do. It's not an ideal situation, regardless. But I would go with the single phase transformer, with a 120/240V secondary.

Welcome to the forum.

 

[jimday]

I would try to get them to sell the 600V gen and buy a single phase genset with the right configuration. Probably only need a 100kW to support the 400A at 240V, 1 phase. They might be able to sell the 600V and pick up a surplus gen from the same place. At a minimum the correctly rated generator would save space, a transformer and a fair amount of installation labor.....

 

[Bdan]

Thanks for the quick responses!
I will definatley suggest they sell the 600 V gen set and buy the appropriate one. Failing that though I am curious as to what might happen to the 3 ph gen set on a single phase load. Will the bearings on the generator fail early or is there some other hazard that I could tell them about?
As far as using a three phase or single phase transformer, I will use the single phase.

Bdan

 

[nawao]

Three phase genny on single phase load

Three phase genny on single phase load

288 Kva is the appropriate three phase generator for a load of 400A at 415/240 Volts. Since the load is pure single phase load you must split the load between the three phases and neutral as much balanced as possible.

 

[Bdan]

I thought the math would be IxE=W in a single phase circuit
So 400 A X 240 V = 96000 watts

Am I wrong?

I Talked to the gen-set manufacturer, they can swap out the 600 volt alternator for a 120/240 volt 1 phase one for about $5,000.00. That will save me from buying a transformer and as Jimday states a lot of labour costs.

Thanks.

Bdan

 

[topgone]

I thought the math would be IxE=W in a single phase circuit
So 400 A X 240 V = 96000 watts

Am I wrong?

I Talked to the gen-set manufacturer, they can swap out the 600 volt alternator for a 120/240 volt 1 phase one for about $5,000.00. That will save me from buying a transformer and as Jimday states a lot of labour costs.

Thanks.

Bdan

Is the 400 amps you mentioned the steady state load? If it is, then you need more than what your math tells you. Keep in mind that motor loads need more genset capacity. Big motors require more starting capacity or you'll have flickers when these runs. Worst case is you losing your power when big motors kick in.

 

[Generatorman]

Is the generator a 12, 10 or 6 lead? (Most likely a 6)
If was a 12 lead (Which if it's a 600V unit that most likely NOT the case) BUT if it was, it can be reconnected to 120/240 single, the kw must be de-rated though.
Maybe keep that in mind if your looking around at new or used back halves, some time folks sell off used 480V/208V/240V 3 phase 12 lead back halves because they do not know that.