GATE EE 2014 Set 1 — Question 53
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Power Systems → Power System Protection → Overcurrent Protection
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Question
The overcurrent relays for the line protection and loads connected at the buses are shown in the figure.
The relays are IDMT in nature having the characteristicThe maximum and minimum fault currents at bus B are 2000 A and 500 A respectively. Assuming the time multiplier setting and plug setting for relay to be 0.1 and 5A respectively, the operating time of (in seconds) is ____________
Correct answer
0.21 to 0.23
Solution
Relay is located on the line segment BC. The normal current through this line is the load at bus C, which is 100 A. Assuming the CT ratio for relay is based on this load, CT ratio = .For a fault current of 2000 A seen by the relay, the Plug Setting Multiplier (PSM) is:The operating time is calculated using the given characteristic:Thus, the operating time of relay is approximately 0.227 seconds.
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