GATE 2014 EE (EE2) – Question 53
A three-phase 100 MVA, 25 kV generator has a solidly grounded neutral. Its positive-, negative- and zero-sequence reactances are 0.2,0.2,0.05 pu on machine bases. A bolted single-phase-to-ground fault occurs at its unloaded terminals. Find immediate fault-current magnitude (A).
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Correct answer: 15300 to 15500
Explanation
An unloaded generator has prefault positive-sequence voltage1pu. The sequence networks are in series for a grounded single-line fault,so If=3/(j(0.2+0.2+0.05)),whose magnitude is6.66667pu. Base current is100MVA/(√3×25kV)=2309.401A. The fault-current magnitude is **15396.0A**.