Formula 3 phase amps from watts

I=KVA*1000/(V*(root 3)) where V is the line to line voltage (208) This gives 666A

-- Don Kelly snipped-for-privacy@peeshaw.ca remove the urine to answer

Not on MY slide rule! I get 222A

ARM

Alan McClure wrote in news: snipped-for-privacy@gwis.com:

Hello,

If the line to line voltage is 208V, then three legs @ 120V will give

666.17 Amps. We should note that this is a total current for the generator. Namely, each leg can supply a current of approx. 222.05 Amps. So both of you are correct; it depends on what you consider to be your reference.

Regards, Bill

R-O-T is 2.8 amps/lVA at 208V 3ø >> 80x2.8=222.3 amps

--s falke

Three phase currents aren't typically specified summed up. There is nowhere in a 3 phase system where a current of 666 amps can be read with a clamp-on meter, for example. Breakers and conductors are sized based upon the phase current (222A).

My calculator gets than answer too. 80,000/3 = 26'666. 26,666/120 = 222 amps per phase

thats assuming is a 3 phase generator of course (from 208 volts).

Although I agree that each phase can carry 222.05 amps, there is no way to combine the three phases to supply a 666.17 Amp load. The vector sum of the three 222.05Amp phases would be zero (ideally).

When rating three-phase equipment, I've always seen the line current used, not 3X that value. Line-line voltage and balanced line current is the normal way to describe their ratings.

Most 3-phase generators are also limited on the amount of imbalance they can tolerate. This unit probably cannot be used to power a single phase load at

222 Amps on only one phase with the others unloaded. Such an unbalance would likely burn the rotor. I've seen imbalance limits of 5 to 15% depending on the size of the unit, but others may tolerate more (or less).

daestrom

don't forget the power factor of the generator. Probably 90% or less.

222.3*.90= 200.07

You have, probably, at full load a 200 amp generator maybe a little less

"Paul Hovnanian P.E." wrote in news: snipped-for-privacy@Hovnanian.com:

I certainly agree, but in terms of what the generator is capable of producing, the total current is 666 Amps. (1.0pf)

Bill

I wondered if anyone would jump on that. The OP stated 80 KVA which is apparent power NOT true power (KW). Power factor does not come into play.

222.3 amps is the correct answer if it is a 3 phase generator. ARM

The power factor in this case doesn't matter, the generator was rated at 80kVA, not 80kW. Assuming the prime mover is large enough, you have

222 amps total available, whether you run a capacitor bank or tungsten lamps. You dont need to know power factor when calculating amps from kva when you know the voltage.

cheers James

One thing to realize in 3 phase systems is that three separate 200A single phase loads will produce a load at each pole of well over 200A (200 * 1.7 in fact, which is 346 amps) . You can't ever get more than 222A from each phase of this generator. You can run three separate

128A single phase 208V loads on each phase at one. This will produce a load of 222A for each phase from the generator because loads on adjacent phases add to each other by a factor of 1.7.

So if you were a marketing guy, you could say this generator will run 128*3 or

384 amps, but that would be typical marketing misleading. But notice that the VA still comes to 80 KVA when used with 3 separate single phase loads. No matter how you slice it, you shouldn't ever get more than 80 KVA from an 80 KVA generator.

-- Mark Kent, WA

You are absolutely correct. I am embarrassed -I apparently multiplied by root(3) rather than dividing. - I blame it on the wine :)

-- Don Kelly snipped-for-privacy@peeshaw.ca remove the urine to answer

No 3-phase generator that I've ever seen (and I've seen quite a few, induction, synch., wound-rotor, motors and generators) would ever have a current rating calculated as 3X line current. If you add the three phase currents of the generator while running at 1.0pf you get zero, not 666.

Machine ratings are by the line current in each phase, not some cockymaimee adding of all three line currents together. If you use your 666 Amps and the line voltage to figure the machines kVA, you get the wrong answer (unless you make up your own formula and don't use the ones standard in the industry).

daestrom

For the benefit of the OP we should mention that the generator will only supply the rated 222A per phase to certain loads. If he's determining whether a certain gen size is 'adequate' he needs to talk to a supplier or engineer because there are issues beyond rated kVA. Of course he's welcome to ask more Q's here first. j