2
3
4
6
Answer is Right!
Answer is Wrong!
Synchronous motors
72. In a synchronous motor, the magnitude of stator back e.m.f. Eb depends on
load on the motor
d.c. excitation only
both the speed and rotor flux
none of the above
Answer is Right!
Answer is Wrong!
Detailed SolutionIn a synchronous motor, the magnitude of stator back e.m.f. Eb depends on
73. The mechanical displacement of the rotor with respect to the stator, in polyphase multipolar synchronous motors running at full load, is of the order of
zero degree
two degrees
five degrees
ten degrees
Answer is Right!
Answer is Wrong!
74. When the field of a synchronous motor is under-excited, the power factor will be
leading
lagging
unity
zero
Answer is Right!
Answer is Wrong!
Detailed SolutionWhen the field of a synchronous motor is under-excited, the power factor will be
75. In a synchronous motor it the back e.m.f. generated in the armature at noload is approximately equal to the applied voltage, then
the motor is said to be fully loaded
the torque generated is maximum
the excitation is said to be zero per cent
the excitation is said to be hundred per cent
Answer is Right!
Answer is Wrong!
76. Which of the following methods is used to start a synchronous motor ?
Damper winding
Star-delta starter
Damper winding in conjunction with star-delta starter
Resistance starter in the armature circuit
Answer is Right!
Answer is Wrong!
Detailed SolutionWhich of the following methods is used to start a synchronous motor ?
77. Slip-rings in a synchronous motor carry
direct current
alternating current
no current
all of the above
Answer is Right!
Answer is Wrong!
78. A synchronous motor develops maximum power when load angle is
45°
60°
90°
120°
Answer is Right!
Answer is Wrong!
Detailed SolutionA synchronous motor develops maximum power when load angle is
79. When the excitation of an unloaded salient pole synchronous motor suddenly gets disconnected
the motor stops
it runs as a reluctance motor at the same speed
it runs as a reluctance motor at a lower speed
none of the above
Answer is Right!
Answer is Wrong!
80. The minimum armature current of the synchronous motor corresponds to operation at
zero power factor leading
unity power factor
0.707 power factor lagging
0.707 power factor leading
Answer is Right!
Answer is Wrong!
Detailed SolutionThe minimum armature current of the synchronous motor corresponds to operation at