Consider the power system shown in Figure 2.27. The pu impedances of the two line sections and the generator are shown in the figure. Concentrating on three-phase faults only, assume that the relay at bus A is set to pickup for a fault at bus C.

Assuming that the pickup setting is equal to one-third of the fault current, what is the pickup setting of this relay? If the dropout-to-pickup ratio for the relay is 0.1, what is the maximum load current at bus B for which the relay will drop out after the fault at bus C is cleared by the protection at B? Recall that after the protection at B clears the fault at C, the current seen by the relay at A is equal to the load connected to bus B, and if the relay does not drop out at this current level, the relay at A will trip its breaker on the load current.

(jo.1) (jo.2) (jo.2) R A A B C Figure 2.27 System diagram for Problem 2.10