This is a fault current problem asking for the generator's contribution at the secondary of the transformer. The subtransient impedance of the generator is .39, rated power is 11MVA. The transformer is rated 5kV/25kV, 6MVA, and 6% . The generator is connected to the low side of the transformer, assume loss-less conductors.
Choosing 6MVA and 25kV as bases;
Zpu-gen = .39(5/25)2(6/11)
= .00851pu
Isc = 1/.00851
= 117.51pu
Ibase = 6MVA/25kVA
= 240
I = 117.51*240
= 28202.4 Amps
28202.4 was not an answer choice. Where did I go wrong? Should the Ibase equation be [6MVA/(25kVA/sqrt3)]
Choosing 6MVA and 25kV as bases;
Zpu-gen = .39(5/25)2(6/11)
= .00851pu
Isc = 1/.00851
= 117.51pu
Ibase = 6MVA/25kVA
= 240
I = 117.51*240
= 28202.4 Amps
28202.4 was not an answer choice. Where did I go wrong? Should the Ibase equation be [6MVA/(25kVA/sqrt3)]