# ONLINE Multiple Choice Questions EE-Synchronous Motors PART 5

61. The size of a synchronous motor decreases with the increase in
(A) speed
(B) horse power rating
(C) flux density
(D) all of the above.

62. The flux density used in synchronous motor is around
(A) 0.05 to 0.46 wb/m2
(B) 0.5 to 0.6 wb/m2
(C) 5 to 6 wb/m2
(D) 50 to 60 wb/m2.

63. In a synchronous motor if the saturation is neglected, then the short
circuit ratio (SCR) will be related to the synchronous reactance (xd) as
(A) SCR
(B) SCR = (xd)2
(C) SCR = 1/ (xd)2
(D) SCR = 1/ (xd).

64. In synchronous motor out of the following losses, which one will have
the highest proportion ?
(A) Stator copper losses
(B) Friction and windage losses
(C) Eddy current losses
(D) Iron losses.

65. Which of the following losses is not dissipated by the stator core
surface in a synchronous motor ?
(A) Copper losses in the slot portion of the conductors
(B) Eddy current losses in the conductors
(C) Iron losses in the stator
(D) Windage losses.

66. The speed of a synchronous motor
(D) always remains constant.

67. Which of the following devices can be used as a phase advancer ?
(A) 3 phase induction motor squirrel cage type
(B) 3 phase induction motor-slip ring type
(C) Synchronous motor working at leading power factor
(D) Synchronous motor working at lagging power factor.

68. When a synchronous motor is connected to an infinite bus, while
operating on leading power factor .
(A) the excitation voltage will be less than the supply voltage
(B) the excitation voltage will be more than
the supply voltage
(C) the excitation voltage will be equal to
the supply voltage
(D) the excitation voltage will be
independent of the supply voltage.

69. In a
synchronous motor
(A) total number of rotor slots = total
number of stator slots
(B) total number of rotor slots is more than
total number of stator slots
(C) total number of rotor slots is less than
the total number of stator slots.

70. In a
synchronous motor during hunting if the rotor speed becomes more than the
synchronous speed
(A) negative phase sequence currents are
generated
(B) harmonics are developed in the armature
circuit
(C) damper bars develop induction generator
torque
(D) field excitation increases.

71. If a
synchronous motor fails to pull into synchronism after applying dc field
current, the probable clause may be
(A) high core losses
(B) low field current
(C) high field current
(D) low short circuit ratio.

72. In
case of a 3 phase synchronous motor, maximum speed variation is
(A)
10%
(B) 5%
(C) 3%
(D)
zero.

73. The
synchronous motors are not self-starting because
(A)
stator
is not used
(B) starting winding is not provided
(C) the direction of instantaneous torque on
the rotor reverses after half cycle
(D) there is no slip.

Questions 74 to 75 refer
to the Figure.

74. In the figure above, the curves for leading power factors are
(A) A and B
(B) C and D
(C) On left of line XY
(D) On right of line XY