1ph vs 3ph?

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kholland

Member
Would these be true statements regarding purely resistive or dc loads:
When using single-phase vs three-phase, the available power for a given 3ph load would be have to be increased 73.2%(.7320508)for the same load at single-phase.
10000/240=41.66
10000/240 X 1.732=24
24 X 1.732=41.66
?

A given load (resistive or dc) uses only 57.7% of the power it uses at single-phase that it does at three phase.
10kVA load @ 240V,1ph =41.66A
10kVA load @ 240V,3ph =24
41.66 X .577 = 24
?

I'm not young enough to know everything.
:) :roll:
 

bob

Senior Member
Location
Alabama
Re: 1ph vs 3ph?

You might need to turn your thinking around a bit.

Assume you have a load = to 24000 watts and you may use 240 volts 3 phase or single phase.

Single phase current = 24000/240 = 100 amps
three phase currrent = 24000/(240 x 1.73)= 57.8 a
The current has been reduced from 100 - 58 = 42 a
You can deliver the same amount of power using
3 phase with reduced amps and reduced voltage drop
over a smaller conductor.
 

charlie b

Moderator
Staff member
Location
Lockport, IL
Occupation
Retired Electrical Engineer
Re: 1ph vs 3ph?

I?d suggest turning around the thinking one more time. If you have a given load, you won?t have a choice of whether to supply it with single phase power or with three phase power. It is already built, and it needs one or the other. The question that you are really asking relates to the formulas for power. Your numbers are right. The single phase power formula is P = E x I. The three phase power formula is P = E x I x (the square root of 3). To seven significant digits, the square root of 3 is 1.7320508. The reciprocal of this number is .05774, or about 57.7%.
 
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