GATE EE 2020 Set 1 — Question 18
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Power Systems → Fault Analysis → Distance Protection
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Question
A lossless transmission line with pu reactance per phase uniformly distributed along the length of the line, connecting a generator bus to a load bus, is protected up to of its length by a distance relay placed at the generator bus. The generator terminal voltage is pu. There is no generation at the load bus. The threshold pu current for operation of the distance relay for a solid three phase-to-ground fault on the transmission line is closest to:
Correct answer
(D) 6.25
Solution
The total reactance of the transmission line is pu. The distance relay is set to protect of the line length. Therefore, the reactance seen by the relay at its reach point is:Given the generator terminal voltage pu and no generation at the load bus, the fault current for a solid three-phase fault at the reach point is:This current represents the threshold above which the relay will operate for faults within its protected zone.
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