A 50 MVA, 10 kV, 50 Hz star-connected unloaded alternator has synchronous reactance 1 pu and subtransient reactance 0.2 pu. For a three-phase terminal short circuit, the ratio of initial to final sinusoidal current amplitudes is ________.
The initial symmetrical AC component is controlled by subtransient reactance: Iinitial=E/Xd″. The final steady component is E/Xd.
Their ratio is Xd/Xd″=1/0.2=**5**. The DC offset, if any, is not part of the sinusoidal component being compared.
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