B:A 20 MVA transformer which may be called upon to operate at 30% overload, feeds 11 KV busbars through a circuit breaker: other circuit breakers supply outgoing feeders. The transformer circuit breaker is equipped with L000/5 A CTs and the feeder circuit breakers with 400/5 A CTs and all sets of CTs feed induction type over current relays. The relays on the feeder circuits breakers have a 125% plug setting, and 0.3 time setting. If 3 ph fault current of 5000 A flows from the transformer to one of the feeders, find the operating time of the feeder relay, the minimum plug setting of the transformer relay and its time setting assuming a discrimination time margin of 0.5 sec. Relays having the following characteristics for TMS-1 PSM T in sec. 2 3.6 5 10 15 20 10 6 3.9 2.8 2.2 2.1

Introductory Circuit Analysis (13th Edition)
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ISBN:9780133923605
Author:Robert L. Boylestad
Publisher:Robert L. Boylestad
Chapter1: Introduction
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B:A 20 MVA transformer which may be called upon to operate at 30% overload, feeds 11 KV
busbars through a circuit breaker: other circuit breakers supply outgoing feeders. The transformer
circuit breaker is equipped with L000/5 A CTs and the feeder circuit breakers with 400/5 A CTs and
all sets of CTs feed induction type over current relays. The relays on the feeder circuits breakers
have a 125% plug setting, and 0.3 time setting. If 3 ph fault current of 5000 A flows from the
transformer to one of the feeders, find the operating time of the feeder relay, the minimum plug
setting of the transformer relay and its time setting assuming a discrimination time margin of 0.5
sec. Relays having the following characteristics for TMS-1
PSM
T in sec.
2 3.6
5
10 15
20
10
6
3.9
2.8
2.2
2.1
Transcribed Image Text:B:A 20 MVA transformer which may be called upon to operate at 30% overload, feeds 11 KV busbars through a circuit breaker: other circuit breakers supply outgoing feeders. The transformer circuit breaker is equipped with L000/5 A CTs and the feeder circuit breakers with 400/5 A CTs and all sets of CTs feed induction type over current relays. The relays on the feeder circuits breakers have a 125% plug setting, and 0.3 time setting. If 3 ph fault current of 5000 A flows from the transformer to one of the feeders, find the operating time of the feeder relay, the minimum plug setting of the transformer relay and its time setting assuming a discrimination time margin of 0.5 sec. Relays having the following characteristics for TMS-1 PSM T in sec. 2 3.6 5 10 15 20 10 6 3.9 2.8 2.2 2.1
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