Fault Currents

[kwainwright]

Four (4) - 3 phase,1000kW generators connect to a syn. Board. 480V, Rated current 1503.51A, P.F.- 0.8, DutyRIME , Sync speed 1800, Subtransient- direct axis Xd" per unit-0.1384 , ohms - 0.0255

What is the fault current at the syn. Board?

 

[spsnyder]

Show us some of your work/thoughts on how to start.

 

[spsnyder]

This may provide some guidance....

http://www.cumminspower.com/www/literature/technicalpapers/PT-6008-GeneratorReactances.pdf

 

[mayanees]

...

...

quicky calc...
43,365 A 3P
42,139 A SLG

 

[ghostbuster]

I have 4 similar units at 600 volts,fault current is 30-40 ka. on the decrement curve.

 

[ron]

Answer already given, but take the full load current of all of the machines and divide that by the subtransient reactance. 43KA+

 

[kingpb]

Answer already given, but take the full load current of all of the machines and divide that by the subtransient reactance. 43KA+

You are correct that this will achieve the approximate answer. However, to clarify for others that may not understand your process; is that by summing the rated currents of all the machines and dividing by the subtransient reactance, in essence you are using 1/4 of the the total reactance, which is the same result as combining the identical reactances of the 4 generators in parallel. Which, would then result in 1/4 the reactance of one of the generators.

Otherwise, if they wer not all the same you have to combine the reactance by taking the inverse of the sum of the individual inverses.