Switchgear and Protection MCQ

21. A fault current of 2,000 A is passing on the primary side of a 400/5 C.T. On the secondary side of the C.T., an inverse-time over current relay is connected whose plug setting is set at 50%. The, plug setting multiplier will be :

(a) 25
(b) 50
(c) 10
(d) 30

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

(a) saturation of the magnetic circuit.
(b) proper mechanical design.
(c) appropriate time-delay element.
(d) electromagnetic damping.

23: Earth fault relays: are

(a) directional relays.
(b) non-directional relays.
(c) short operate time relays.
(d) none of these.

24. The domains of power system where directional overcuuent relay is indispensable are

(a) in case of parallel feeder protection.
(b) in case of ring main feeder protection.
(c) both (a) and (b).
(d) none of the above

25. Directional overcurrent relays have two exciting coils connected across

(a) CT secondaries of two different phases.
(b) VT secondaries of two different phases.
(c) CT and VT secondaries of the same phase.
(d) CT and VT secondaries of two different phases.

26. Consider the following statements. Distance relays used for protection of transmission lines might operate undesirably due to

1. magnetizing-current inrush.
2. power swings.
3. series compensating capacitors.
4. switching overvoltages.

Of these statements
(a) 1 and 2 are correct.
(b) 2 and 3 are correct.
(c) 1, 2 and 4 are correct.
(d) 1, 3 and 4 are correct.

27. In distance protection, the relay measures

(a) negative sequence impedance of the line from relay up to the fault point.
(b) positive sequence impedance of the line from relay up to the fault point.
(c) self impedance of the line from relay up to the fault point.
(d) zero sequence impedance of the line from relay up to the fault point.

28. If the fault occurs near the relay, the V/I ratio will be

(a) lower than that of if the fault occurs away from the relay.
(b) constant for all distances.
(c) higher than that of the fault occurs away from the relay.
(d) none of the above.

29. Impedance relay may use

(a) balance beam structure.
(b) induction-cup structure.
(c) shaded pole structure.
(d) either (a) or (b).

30. Impedance relay can be used for

(a) phase faults only.
(b) earth faults only.
(c) both earth and phase faults.
(d) none of above.

31. An impedance relay is a

(a) voltage restrained overcurrent relay.
(b) voltage restrained directional relay.
(c) directional restrained overcurrent relay.
(d) directional restrained overvoltage relay.

32. Threshold characteristics of a plain impedance relay in a complex Z plane is a

(a) circle passing through origin.
(b) circle with the centre at the origin.
(c) straight line passing through origin.
(d) straight line offset from the origin.

33. On transient fault OC and impedance relay.

(a) under reaches.
(b) over reaches.
(c) reach unaffected.
(d) none of these.

34. The structure used in reactance relays is

(a) induction cup.
(b) double induction loop.
(c) single induction loop.
(d) either (a) or (b).

35. A reactance relay is

(a) voltage restrained overcurrent relay.
(b) voltage restrained directional relay.
(c) directional restrained overcurrent relay.
(d) directional restrained overvoltage relay.

36. The operating characteristics of a reactance relay in the complex impedance plane is a

(a) circle with its origin at the centre of the R – X plane.
(b) circle passing through the origin.
(c) straight line passing through the origin.
(d) straight line parallel to the X-axis.

37. Reactance relay is normally used for protection against

(a) earth fault only.
(b) phase fault only.
(c) both earth and phase faults.
(d) none of the above.

38. Admittance relay is

(a) non-directional relay.
(b) directional relay.
(c) differential relay.
(d) none of these.

39. A mho relay is a

(a) voltage restrained directional relay.
(b) voltage restrained overcurrent relay.
(c) directional restrained overcurrent relay.
(d) directional restrained overvoltage relay.

40. For ground fault use prefer:

(a) plain impedance relay.
(b) directional relay.
(c) reactance relay.
(d) over current relay.