How do you size a 3 phase 550 KVA generator?

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kda3310

kda3310

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Dry Prong, Louisiana
I am over seas and have a generator that is rated in KVA. Or so the generator mechanics say it is. The generator is 550 KVA 3 phase with a line to line voltage of 400 volts and a line to neutral voltage of 230 volts at 50hz. How do I size the generator and when I size it is it per leg or do I have to divide it by three to get the amperage per leg.

Jason
 
550kVa results in a current of 793 amps per phase at 400 volts. I think you should install at least three -3 cond. cable 300MCM

Good luck

Devosts
 
kda3310 said:
I am over seas and have a generator that is rated in KVA. Or so the generator mechanics say it is. The generator is 550 KVA 3 phase with a line to line voltage of 400 volts and a line to neutral voltage of 230 volts at 50hz. How do I size the generator and when I size it is it per leg or do I have to divide it by three to get the amperage per leg.Jason
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You have a 550 kva generator. Nothing to size. If you are asking what is the
max amperage output you need to caculate it. 550kva/(.400 x 1.73) = 795 amps. If you want the conductor to match the max output check you code book and table 310.16. It looks like 2 600 cu per phase will provide you 840
amps per phase. You may want to caculate the actual load and base you caculations on that figure.
 
Yes, I am trying to fined how many amps it is good for. If it is good for 800 amps then do I need to size it with a 800 amp overcurent divice or do I divide that by three.

Jason
 
It would be a 3-pole 800A device.

My understanding of IEC equipment is that all breakers are 100% rated, so there would be no need to increase it by 125% as is done in the US to meet NEC.
 
kda3310 said:
Yes, I am trying to fined how many amps it is good for. If it is good for 800 amps then do I need to size it with a 800 amp overcurent divice or do I divide that by three.

Jason
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I'm guessing your in Iraq like I am. I agree that this generator requires an 800A breaker with (2) runs of 4/C 240mm cable. This is the largest size conductor I've seen in Iraq for LV applications. Its rated at about 440A per run.

On a side note. I'm willing to bet that the generator in question is much larger than required for the connected load. I see this all the time over here. Then again, the contractor responsible for generator maintenance gets paid by the KVA. It's my job to make reccomendations for generator downsizing and generator consolidations (basically forming mini-grids.)
 
kda3310 said:
I am over seas and have a generator that is rated in KVA. Or so the generator mechanics say it is. The generator is 550 KVA 3 phase with a line to line voltage of 400 volts and a line to neutral voltage of 230 volts at 50hz. How do I size the generator and when I size it is it per leg or do I have to divide it by three to get the amperage per leg.

Jason
Click to expand...
Do you have a current code book? Read artical 445 and yes don't forget about 1.73
 
The exception to 445.13 whereby the conductors do not have to be sized larger then the rating as long as protection eliminates possible overloading, would most likely apply.
 
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