ELECTRICAL MACHINE DESIGN 6

51. Damper winding is used to
a) reduce air gap harmonics flux
b) reduce oscillations
c) increase stability limits
d) resist the moisture
ans. b

52. When a synchronous generator is designed with lower SCR it
a) will give higher stability limit
b) will have lower SC current
c) will give better voltage regulation
d) will have high synchronous power
ans.b

53. An alternator with higher value of SCR has
a) poor voltage regulation and lower stability limit
b) better voltage regulation and higher stability limit
c) poor voltage regulation and higher stability limit
d) better voltage regulation and lower stability limit
ans. b

54. Under short circuit conditions, the power factor of a synchronous machine is
a) 1
b) about 0.8 lagging
c) almost zero lagging
d) 0.5
ans.c

55. If the stator winding of a 3-phase induction motor is delta connected the rotor winding
a) should be delta connected
b) should be star connected
c) should not be delta connected
d) may be delta or star connected
ans. d

56. An increase in number of poles of an induction motor results in
a) decrease in maximum pf
b) increase in maximum pf
c) no change in maximum pf
d) cannot be predicted
ans. a

57. The effect of leakage flux in case of 3-phase induction motor is to
a) reduce the torque produced
b) increase the torque produced
c) increase the operating power factor
d) none of the above
ans.a

58. For a 3-phase 50 Hz 4 pole induction motor having rotor diameter of 35 cm, the peripheral speed is
a) 20.1 m/s
b) 24.2 m/s
c) 26.9 m/s
d) 32.3 m/s
ans. c

59. Air gap of a polyphase induction motor is kept small to a
a) reduce the possibility of crawling
b) reduce the noise
c) reduce magnetizing current
d) obtain high starting torque .
ans. c

60. If an induction motor is designed with lesser air gap, then the motor will have
a) better cooling
b) better overload capacity
c) better power factor
d) lower power factor
ans. c