Secondary Fault Current

let me give you some information.

1-there is no primary or secondary current in generator, just current.

to find short circuit current, there are two ways.

first, you need to contact your generator manufacturer and ask them for the subtransient reactance (xd") of the generator and also they might tell you the amount of shortcircuit current.

if it is not available,

Second:
If you want to do calculation you have to follow the following steps.

1- check the nameplate of the generator which is usually marked with its subtransient reactance Xd". This short circuit value occurs immediately after a short circuit and lasts for a few cycles and it is essential for short circuit calculation because it produces the most short circuit current.

Just simple

Short Circuit kVA = generator kVA rating / Xd" rating

Incase there are more than one sources of short circuit current present in a system, the total amount of short circuit kVA is the sum of various sources.

for example:

if two 7625-kVA, 138-kV, Xd"=0.17, synchronous generators cogenerating into an electrical system and this electrical power system is also supplied from an electrical utility with 300 MVA, the total available fault kVA at the terminal of generator equals to

Total fault kVA = 2(7265kVA/0.17) + 300 MVA = 385470 kVA.

you need all positive, negative and zero sequence impedance. A lot of generators Isc-SLG fault current is higher than the 3 phase fault due to such a low zero sequence current.

Yes, if we want to do line to Neutral fault calculation then we have to consider the positive, negative as well as zero sequence.

Three phase fault: Isc = E / (1.732*X"d)

Line to Neutral fault: Isc = E * 1.732 / ( Xd" + X2 + Xo)

where
E: generator line to line voltage before fault, volts
X"d: generator direct axis subtransient reactance, ohms
X2 : generator negative sequence reactance, ohms
Xo : generator zero sequence reactance, ohms

so, we have to do calculation and also see generators grounding type.

I forgot to logg in and replied in above comment.

Yes, if we want to do line to Neutral fault calculation then we have to consider the positive, negative as well as zero sequence.

Three phase fault: Isc = E / (1.732*X"d)

Line to Neutral fault: Isc = E * 1.732 / ( Xd" + X2 + Xo)

where
E: generator line to line voltage before fault, volts
X"d: generator direct axis subtransient reactance, ohms
X2 : generator negative sequence reactance, ohms
Xo : generator zero sequence reactance, ohms

so, we have to do calculation and also see generators grounding type.

thanks for the help.

What is generator?

Mythical creature from the 80's