Switchgear and Protection MCQ

41. A distance relay is said to be inherently directional if its characteristics on R – X diagram

(a) is a straight line off-set from the origin.
(b) is a circle that passes through the origin.
(c) is a circle that encloses the origin
(d) always a separate directional relay is required.

42. For the protection of lines against faults involving variable fault resistance, the preferred relaying scheme is a

(a) plain impedance relay.
(b) directional overcurrent relay.
(c) mho relay.
(d) reactance relay.

43. The relay used for phase fault protection of short transmission lines is

(a) reactance relay.
(b) impedance relay.
(c) mho relay.
(d) IDMT relay.

44. Mho relay is usually employed for the protection of

(a) short lines only.
(b) medium lines only.
(c) long lines only.
(d) any line.

45. Where severe synchronizing swing occur, the relay employed is

(a) impedance relay.
(b) mho relay.
(c) reactance relay.
(d) induction relay.

46. Which of the following relays has inherent directional characteristic?

(a) Mho.
(b) Reactance.
(c) Impedance.
(d) None of the above.

47. For the protection of a very long extra high voltage line, the protective relay used is

(a) overcurrent with extremely inverse characteristics.
(b) percentage differential relay.
(c) reactance type distance relay.
(d) mho type distance relay.

48. A differential relay responds to

(a) algebraic difference of two or more similar electrical quantities.
(b) phasor difference of two or more similar electrical quantities.
(c) algebraic difference between two currents.
(d) algebraic difference between two voltages.

49. Differential relays are used for protection of equipment against

(a) internal faults.
(b) overcurrent.
(c) reverse current.
(d) reverse power.

50. Undervoltage relays are mainly used for

(a) motor protection.
(b) transformer protection.
(c) transmission line protection.
(d) All of these.

51. In a biased differential relay the bias is defined as a ratio of

(a) number of turns of restraining and operating coil.
(b) operating coil current and restraining coil current.
(c) fault current and operating coil current.
(d) fault current and restraining coil current.

52. Differential relays are used for protection of

(a) feeders.
(b) alternators.
(c) transformers.
(d) all of these.

53. Both voltage and current signals are required for

(a) a plain overcunent relay.
(b) a differential relay.
(c) a directional relay.
(d) a biased differential relay.

54. The relay used for feeder protection is

(a) undervoltage relay.
(b) Translay relay.
(c) thermal relay.
(d) Buchholz relay.

55. In the case of transmission line protection, overcurrent relay is used

(a) only up to 110 kV.
(b) only up to 220 kV.
(c) only up to 50 kV.
(d) only up to 1,100 kV.

56. Phase relays are used to provide protection against

(a) single line to ground fault.
(b) three phase fault only.
(c) phase faults involving two or more phases.
(d) double phase to ground fault only.

57. In a 3-phase circuit, residual current means the flow of………..current.

(a) negative-sequence
(b) zero sequence
(c) dc transient

58. The plug setting of a negative sequence relay is 0.2 A. The current transformer ratio is 5 : 1. The minimum value of line to line fault current for the operation of the relay is

(a) 1 A
(b) 1/1.732 A
(c) 1.732 A
(d) 0.2/1.732 A

59. Zero-sequence current is used for relaying purposes only in the case of

(a) phase overcurrent relay.
(b) phase impedance relay.
(c) ground overcurrent relay.
(d) ground impedance relay.

60. Over conventional electromechanical relays, the transistor relays have the advantages of

(a) low power consumption, less maintenance and greater sensitivity.
(b) quick operation and high reset to pick-up ratio.
(c) wide range of characteristics approaching more or less to ideal requirements.
(d) all of the above.