Electrical Drive MCQ

41. DC series motors are very suitable for heavy duty applications such as electric railways, rolling mills because of

(a) low initial as well as maintenance cost.
(b) high starting torque.
(c) possibility of speed control.
(d) nearly constant speed.

42. A flywheel is normally fitted to

(a) dc series motor driving a constant torque load.
(b) separately excited dc motor driving pulsed torque load.
(c) cumulatively compound motor driving pulsed torque load.
(d) differentially compound motor driving pulsed torque load.

43. Which motor should not be used for centrifugal pumps ?

(a) Shunt.
(b) Series.
(c) Cumulatively compound.
(d) Differentially compound.

44. For continuously running roiling mills with intermittent loading, the most suitable dc drive is

(a) dc series motor.
(b) dc shunt motor.
(c) dc differentially compounded motor.
(d) dc cumulatively compounded motor.

45. For quick speed reversal the motor preferred is

(a) dc motor.
(b) squirrel cage induction motor.
(c) slip-ring induction motor.
(d) synchronous motor.

46. The motor, owing to its inherent characteristics, best suited for the rolling mills is

(a) dc shunt motor.
(b) dc cumulative compound wound motor.
(c) squirrel cage induction motor.
(d) synchronous motor.

47. Squirrel cage induction motors with high slip and slip-ring induction motors develop maximum torque at standstill and are used for

(a) elevators.
(b) machine tools.
(c) presses and punches.
(d) all of the above.

48. Belted slip-ring induction motor is almost invariably employed for

(a) conveyors.
(b) jaw-crushers.
(c) centrifugal blowers.
(d) water pumps.

49. Belted would induction motors are preferred for

(a) gyratory crushers.
(b) screw pumps.
(c) machine tools.
(d) water pumps.

50. The pair used for frequency converters is

(a) squirrel cage induction motor and synchronous motor.
(b) slip-ring induction motor and synchronous motor.
(c) slip-ring induction motor and squirrel cage induction motor.
(d) all of above.

51. For the same rating, the size of the single-phase induction motor is about……….that of the corresponding three-phase induction motor.

(a) three times
(b) the same as
(c) 1.5 times
(d) one-third

52. A fluctuating voltage supply is detrimental to a refrigerator motor but not to a ceiling fan, although both are single-phase induction motors because, the refrigerator motor

(a) is made more robust than the fan motor.
(b) is subjected to short-duty cycle but the fan motor is subjected to continuous duty.
(c) is enclosed in a sealed unit while the fan motor is open to the environment.
(d) load is constant, but the fan motor load is voltage dependent.

53. Ward-Leonard controlled dc drives are usually used for……duty excavators.

(a) light
(b) medium
(c) heavy

54. Speed control by variation of field flux results in

(a) constant power drive.
(b) variable power drive.
(c) constant torque drive.
(d) variable torque drive.

55. In variable speed dc motor drive the armature voltage control leads to

(a) constant power operation.
(b) constant torque operation.
(c) variable torque operation.
(d) randomly varying power operation.

56. Speed of an induction motor is controlled by injecting voltage into the rotor winding. Frequency of the injected voltage should be

(a) main frequency.
(b) frequency corresponding to required speed.
(c) frequency corresponding to rotor speed.
(d) slip frequency

57. The slip power recovery scheme is used in induction motor for speed control in the range

(a) above synchronous speed.
(b) below synchronous speed.
(c) both above and below synchronous speed.
(d) none of the above.

58. The electric braking system commonly employed in rolling mills, elevators and printing presses is

(a) plugging.
(b) rheostatic.
(c) dynamic.
(d) regenerative.

59. For rheostatic braking of two series motors connected in parallel

(a) cross-connection is better.
(b) equaliser connection is better.
(c) both are equally good.
(d) none of the two is required.

60. Dynamic braking is employed to brake

(a) non-reversing drive.
(b) reversing drive.
(c) in both (a) and (b).