For the three-bus power system shown in the figure, the trip signals to the circuit breakers  to  are provided by overcurrent relays  to , respectively, some of which have directional properties also. The necessary condition for the system to be protected for short circuit fault at any part of the system between bus 1 and the  -  loads with isolation of minimum portion of the network using minimum number of directional relays is

A power system with two generators is shown in the figure below. The system (generators, buses and transmission lines) is protected by six over current relays  to . Assuming a mix of directional and non directional relays at appropriate locations, the remote backup relays for  are

The over current relays for the line protection and loads connected at the buses are shown in the figure.

The relays are IDMT in nature having the characteristic

The maximum and minimum fault current at bus B are 2000A and 500A 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 _______________.

Consider the protection system shown in the figure below. The circuit breakers, numbered from 1 to 7 are of identical type. A single line 10 ground fault with zero fault impedance occurs at the midpoint of the line (at point F), but circuit breaker 4 fails to operate ("stuck breaker"). If the relays are coordinated correctly, a valid sequence of circuit breaker operations is

In an inverse definite minimum time, electromagnetic type over-current relay the minimum time feature is achieved because of

If the fault current is 2000A, the relay setting is 50% and CT ratio is 400:5, the plug setting multiplier will be

The distribution system shown in figure is to be protected by over current system of protection.

For proper fault discrimination directional over current relays will be required at locations