Switchgear and Protection MCQ PDF Download

41. For a transmission line the standing wave ratio is the ratio of

(a) peak voltage to rms voltage.
(b) maximum current to minimum current.
(c) maximum voltage to minimum voltage.
(d) maximum impedance to minimum impedance.

42. The steepness of the wavefront can be reduced by connecting

(a) an inductor in series with the line.
(b) a capacitor between line and earth.
(c) either (a) or (b).
(d) an inductor between line and earth or a capacitor in series with the line.

43. If a travelling wave travelling along a loss-free overhead line does not result in any reflection after it has reached the far end, then the far end of the line is

(a) open circuited.
(b) short circuited.
(c) terminated into a resistance equal to surge impedance of the line.
(d) terminated into a capacitor.

44. A rectangular voltage wave is impressed on a loss-free overhead line, with the far end of the line being short-circuited. on reaching the end of this line

(a) the current wave is reflected back with positive sign, but the voltage wave with negative sign.
(b) the current wave is reflected back with negative sign, but the voltage wave with positive sign.
(c) both the current and the voltage waves are reflected with positive sign.
(d) both the current and the voltage waves are reflected with negative sign.

45. Consider the following statements for transmission lines :

1. When a transmission line is terminated by its characteristic impedance the line will not have any reflected wave.
2. For a finite line terminated by its characteristic impedance the velocity and current at all points on the line are exactly same.
3. For a lossless half wave transmission line the input impedance is not equal to load impedance.

Which of the statements given above are correct ?
(a) 1 and 2 only.
(b) 2 and 3 only.
(c) 1 and 3 only.
(d) 1, 2 and 3.

46. The reflection coefficient for the voltage wave in overhead lines is given as

(a) R_o ÷ (R_o – R_L)
(b) R_L ÷ (R_o – R_L)
(c) (R_L – R_o) ÷ (R_L + R_o)
(d) (R_L + R_o) ÷ (R_o – R_L)

47. The insulation coordination for UHV lines (above 500 kV) is done based on

(a) lightning surges.
(b) lightning surges and switching surges.
(c) switching surges.
(d) none of the above.

48. In comparison to line insulation, the insulation level of the station equipment is

(a) less.
(b) more.
(c) equal.
(d) not related directly with each other.

49. When a wave reaches an open circuit the………at the termination is/are double the incident value(s)

(a) voltage
(b) current
(c) both the voltage and current

51. When a wave reaches a short-circuit the………at the termination is/are zero

(a) voltage
(b) current
(c) both the voltage and current

52. A backward wave means a

(a) negative voltage wave.
(b) negative current wave.
(c) a wave travelling in the negative direction.

53. The size of the earth wire is determined on the basis of

(a) voltage of the service line.
(b) current carrying capacity of the service line.
(c) atmospheric conditions.
(d) none of the above.

54. Neutral earthing is provided for

(a) the safety of personnel from electric shock.
(b) the safety of equipment and personnel against lightning and voltage surges.
(c) reducing the voltage stress on lines and equipment with respect to earth under various operating and fault conditions.
(d) controlling the earth fault currents for protective relaying.
(e) both (c) and (d).

55. Isolated neutral system has the disadvantage(s) of

(a) voltage oscillations.
(b) difficult earth fault relaying.
(c) persistent arcing ground.
(d) all of the above.

56. Isolated neutral transmission system is not recommended as the

(a) system insulation is overstressed due to over-voltages.
(b) insulation overstress may lead to its failure resulting in phase-to-phase faults.
(c) system is not adequately protected against earth fault.
(d) all of the above.

57. Neutral earthing has the advantage(s) of

(a) elimination of arcing grounds.
(b) low maintenance and operating costs over isolated neutral systems.
(c) simplified design of earth fault protection.
(d) discharging of over-voltages due to lightning to earth.
(e) all of the above.

58. The advantage of neutral earthing is

(a) safety of personnel.
(b) reduction of earth fault current.
(c) elimination of arcing ground.
(d) none of the above.

59. Resistance earthing is employed for voltages between

(a) 3.3 and 11 kV.
(b) 11 and 33 kV.
(c) 33 and 66 kV.
(d) 66 kV and 132 kV.

60. Earthing of transformer neutral through reactance will improve its

(a) transient stability.
(b) steady state stability.
(c) both of the above.
(d) none of these.