Three Phase to Single Phase

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santoro

Member
Location
Alaska
Anybody have a clever idea on how to balance a three-phase generator output to a single-phase load using transformer(s)? The generator output is 30 kw three phase, and the single-phase load is 15 kw. The load is currently supplied by a utility voltage (single phase only) of 115/230V. The output of the three phase generator can be 120/208, 127/220, or 139/240. There are both 120 and 230V single phase loads. Goal of exercise is to use generator as backup w/ transfer switch. Would like to keep the backup voltage as close to utility voltage as possible.
Thanks
 
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bennie

Esteemed Member
Re: Three Phase to Single Phase

You will need a 3 phase motor driving a 15 KW single phase generator. Best to get a single phase generator to start with.
 
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santoro

Member
Location
Alaska
Re: Three Phase to Single Phase

No can do, need three phase to start Fire Pump Motor. Have generator and motor. Need to reasonably balance remanding single-phase load (shed when FP is called for). Looking for economical solution. May not be possible but still holding out for ingenious solution.
 
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bennie

Esteemed Member
Re: Three Phase to Single Phase

santoro: Good luck! There is a lot I don't know, I will be interested if someone can resolve your problem.
 
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bennie

Esteemed Member
Re: Three Phase to Single Phase

I have been thinking...Get 3 single phase panels, convert them for 120 volts only. Connect one phase to each panel. I would have to draw out a transfer switch setup. It may be 49 poles before finished :(

Connect the load circuits according to time and duration of each load.

[ June 23, 2003, 08:10 PM: Message edited by: bennie ]
 
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bennie

Esteemed Member
Re: Three Phase to Single Phase

Sorry: I was changing my mind while you were answering. Yes it is important to balance the load on the generator as close as possible.
 
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bennie

Esteemed Member
Re: Three Phase to Single Phase

I didn't think of that hook up. It appears to be an open delta to an open wye. With proper transformers it should work.
 
J

jim dungar

Moderator
Staff member
Location
Wisconsin
Occupation
PE (Retired) - Power Systems
Re: Three Phase to Single Phase

Be careful with the Square D "Hoppy Hookup".

The single phase side is balanced, however the common three phase (think B phase) conductor current is 3x the other phases (think A and C). Your generator will definitly not be balanced.

Also the single phase line to line voltage will be 208V not 240.
 
engy

engy

Senior Member
Location
Minnesota
Re: Three Phase to Single Phase

What am I missing here with the hoppy hookup?
(neutral current same as original 1-ph service?)
(primary common current 3x of other two lines?)

How is this hookup different from normal delta-wye?
(Besides only using 2 of 3 phases)

I assume the "existing" service was 120/240.

What am I not assuming? :confused:

[ July 14, 2003, 04:31 PM: Message edited by: engy ]
 
brian john

brian john

Senior Member
Location
Leesburg, VA
Re: Three Phase to Single Phase

If you want to get really inventative, and possible void the warranty. If this is a 12 wire generator design a contactor system that would connect the generaor single phase under "normal" operatoin. and three phase under "fire pump" ooperation. It is do-able.
 
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