Question

2.10 Consider the power system shown in Figure 2.27. The nu impedances of the two line sections and the perete ure shown in the figure. Concentrating on three-phase faults only, assume that the relay bus A is set to pick up for hus C Assuming that the pickup setting is equal to the third of the wall current what is the pickup setting of this relay? If the dropout-to-pickup rate for the relay is 01. what is the maximum load current bus for which the relay will drop out after the full albus C is cleared by the protection 12 Recall that after the protection B clear the full C, the current seen by the relay al A is equal to the load connected to bus B, and if the relay does not drop out at this current level, the relay MA will trip its heaker on the load current. Pure 2.27 System diagram for Problem 2.10

it is from the book "power system relaying" by Stanley horowitz, 4th edition

Answer 1

Fault at a produces a fault Current of (...)/(0.1 +0.2 +0.2) =2.opu The Pickup Setting for the delay is 2013 = 0.666 Pu The droput Current is yo or 0.0666 Pu This is the maximum load Current that the delay at A will tolerate before it trips (falsely) due to fault at c.