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 o

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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 ________.

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Fault current is inversely proportional to reactance during fault.

$\Rightarrow I_f\propto\frac{1}{X}$

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