GATE EE 2016 Set 2 — Question 23
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Power Systems → Power System Protection → Overcurrent Protection
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Question
A power system with two generators is shown in the figure below. The system (generators, buses and transmission lines) is protected by six overcurrent relays to . Assuming a mix of directional and nondirectional relays at appropriate locations, the remote backup relays for are
Correct answer
(D) R₁, R₆
Solution
From the single-line diagram: generator feeds the left bus, two parallel lines connect the left bus to the middle bus (relays , at the left-bus ends and , at the middle-bus ends), and a third line connects the middle bus to the right bus (relay at the middle-bus end, at the right-bus end) where generator is connected. therefore looks from the middle bus into the lower parallel line; faults on that line are its primary zone. The current it has to interrupt is the contribution that flows from the middle bus into the faulted line.If fails, that contribution must be interrupted one bus further back, at the remote end of every path that feeds the middle bus:
1.Power reaching the middle bus from travels through the right-hand line, whose relay at the remote (right) bus is .
2.Power reaching the middle bus from travels through the upper parallel line, whose relay at the remote (left) bus is .
and are at the same bus as , so they are not remote backups, and is the primary relay at the other end of the same line.Answer: (D) Continue learning with Success Tracker
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