single phase calculations

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mikehughes8

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This may seem elementry but I need the refresher. A 200KW 50Hz (415/240)generator @ .8 PF supplies 3 phase power. For a three-phase load my generator is capable of suppling the following amperage:

200kw / 415*1.73*.8 = 348amps

For single phase loads each leg can supply

200kw / 240*.8 = 1041 amps

Is this 1041 amps per leg A-N, B-N, and C-N or 348 amps A-N, B-N, and C-N

Thanks in advance for the clarification
 
if this helps

phase amps = line amps for wye
so i think your first calc is correct that you have the 348 amps

and to clarify thats A-N, B-N, and C-N on your 240
 
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jjs said:
I don't believe the generator outputs 200KW per leg as the 240V equation you posted seems to assume.
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Duh....thats the knock on the side of the head that I needed. It would sure be nice to get a 3 for 1 deal though.
 
I also did the math here. Your generator is capable of 200KW. So in a 3phase application it would be 348 amps per phase.
In a single phase application, while your math works, the generator is not wired for that. I suspect if you wanted a single phase, you would only be able to deliver 348amps based upon the windings.
Does this help at all ?
Just my $.02
 
Similar question, different voltage?

Similar question, different voltage?

This may also seem elementary, but I wanted to convert from three phase to single phase given a total connected VA of 9600 at 277/480V 3phs. To determine what the single phase VA is on this would I need to pull out the voltage and simply take the result and multiply by 240v?

i.e. 9600VA/(480*1.73) = 11.5A*240V = 2760VA.

Is this the correct conversion. It seems as if I'm missing a step?
 
fgreco2 said:
Is this the correct conversion. It seems as if I'm missing a step?
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Actually, you're adding a step. It's up to you to balance the loading, but if you do, VA = VA.

9600 VA of 1-ph load = 9600 VA @ 3-ph.
 
Still confused

Still confused

Larry,

Not so sure I follow your explanation. 9600VA or 9.6kVA is 3phs load at 277/480V. So this is the same single phase load at 120/240V?
 
fgreco2 said:
Larry,

Not so sure I follow your explanation. 9600VA or 9.6kVA is 3phs load at 277/480V. So this is the same single phase load at 120/240V?
Click to expand...
What I'm saying is, regardless of the voltage, 9.6Kva @ 240v is the same power as 9.6Kva @ 480v. When you transform one voltage to another, and properly adjust components for ampacity, you conserve power.

In other words, if you can somehow use all of the primary's capacity, such as transforming a 480v/3ph feed to a 208/120v-3ph panel, and supplying a balanced group of 120v/1ph loads, then yes, Kva in = Kva out.
 
fgreco2,

Perhaps, the way you phrase the question is part of the confusion.

Think of the 9.6 kVA load as 9600 pounds of rock on a skid.

If I pull the skid with a D-8 Cat or a John Deere tractor, the friction of the skid on the ground remains the same. 9600 pounds of rock on a skid is the same, regardless of what moves it.

Is this a theoretical exercise, or are you thinking about some "real world" equipment?
 
al hildenbrand said:
fgreco2,

Perhaps, the way you phrase the question is part of the confusion.

Think of the 9.6 kVA load as 9600 pounds of rock on a skid.

If I pull the skid with a D-8 Cat or a John Deere tractor, the friction of the skid on the ground remains the same. 9600 pounds of rock on a skid is the same, regardless of what moves it.

Is this a theoretical exercise, or are you thinking about some "real world" equipment?
Click to expand...

It's a real world situation. I'm a bit green with "unique" situations .... still learning. I have a customer that is installing a panel with a voltage rating of 277/480V three phase, and with such a small load 9.6Kva it may be cheaper for them on the "utility" side of the business to serve with single phase 120/240. With what's being mentioned above the power calculated to operate said equipment at 9.6kVA is the requirement, and what vaires is the amperage and the voltage. Understood. Thanks to all for holding my hand.
 
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