Finally, a question I can answer:...By the way, what does POCO mean?...
It may be a minor point, but "transformer could contribute" is probably not the best way to phrase that as it might lead to confusion down the road for some....A 2000kVA, 480V secondary, transformer with 5% impedence could contribute 2408FLA/.05 = 48,000A...
Here's an example of the difference between a generator and a transformer wrt short circuit contributions:
Based on the impedence of the transformer the short circuit contribution is limited or finite. Isca = Xfmr FLA/Xfmr Z. Usually you can find the max contribution from a utility by using this simple formula. We use Z= 5% as a standard inpedence. By the way, what does POCO mean?
A generator is a source capable of delivering current at its rated capacity. So a 1800kW, 480V generator, .9pf, will contribute 2400A.
A 2000kVA, 480V secondary, transformer with 5% impedence could contribute 2408FLA/.05 = 48,000A.
Here's a useful link from the man himself.
http://www.mikeholt.com/documents/calculations/formulas/FaultV6.2.xls
Along this line, I think a better phrase would be 'a transformer lets through' an amount of short circuit current.It may be a minor point, but "transformer could contribute" is probably not the best way to phrase that as it might lead to confusion down the road for some.
You have given full load contribution of the generator. Similar to the transformer, the generator will contribute fault current inversely with its impedance. Typical impedance (subtransient reactance) for an 1800 kW generator would be 0.1 pu so the contribution would be 2400FLA/0.1 = 24,000A.
Interesting. I don't understand how a generator that produces a max current based on the size of its mag field and copper windings can produce more current without changing speed or the field strength.