A 20 MVA Transformer which is used to operate at 30% overload feeds an 11 kV busbar through a circuit breaker (CB) as sh

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A 20 Mva Transformer Which Is Used To Operate At 30 Overload Feeds An 11 Kv Busbar Through A Circuit Breaker Cb As Sh 1 (133.43 KiB) Viewed 3983 times

A 20 MVA Transformer which is used to operate at 30% overload feeds an 11 kV busbar through a circuit breaker (CB) as shown in Fig. 4. The transformer CB is equipped with a 1000/5 CT and the feeder CB with 400/5 CT and both CTS feed IDMT relays having the following characteristics PSM Time (sec) System 2 10 3 6 20 MVA 5 4.1 1000/5 The relay on the feeder CB has PS = 125% and TMS = 0.3. If a fault current of 5000 A flows from the transformer to the feeder, determine 5 A IDM T 10 3 a. operating time of feeder relay. b. Suggest suitable PS and TMS of the transformer relay to ensure adequate discrimination of 0.5 s between the transformer relay and feeder relay. 11 kV 15 PS = ? TMS = ? 20 2.5 2.2 400/5 A 5 A IDM T PS = 125% TMS = 0.3 4 I, = 5000 A