Question

A \(50\;MVA,\;10\;kV,\;50\;Hz\), star-connected, unloaded three-phase alternator has a synchronous reactance of 1 p.u. and a sub-transient reactance of \(0.2\;p.u.\) If a 3-phase short circuit occurs close to the generator terminals, the ratio of initial and final values of the sinusoidal component of the short circuit current is ________.

Answer 1

Fault current is inversely proportional to reactance during fault.

\(\Rightarrow I_f\propto\frac{1}{X}\)

 

\(\Rightarrow \frac{{intial\;current}}{{final\;current}} = \frac{{Synchronous\;reactance}}{{Sub - transient\;reactance}} = \frac{1}{{0.2}}\) \(= 5\)