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Single Line to Ground (L-G) Fault - Unloaded & Loaded

Two identical...

Question

Two identical unloaded generators are connected in parallel as shown below

Both the generators are having positive, negative and zero sequence impedances of 0.6 p.u., 0.4 p.u. and j0.35 p.u. respectively. If prefault voltage is 1 p.u., for a line to ground (L-G) fault at the terminals of the generator, the fault current magnitude in p.u. is______.
(Assume neutral impedance $Z_{n} = j 0.02 p . u .)$
4.36

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Solution

The correct option is A 4.36
Here both the alternators are working in parallel.

$I_{f} = 3 I_{a 1} = \frac{3}{j 0.3 + j 0.2 + j 0.188} = - j 4.36 p . u .$

$| I_{f} | = 4.36 p . u .$

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