Top 150+ Solved Synchronous Motors MCQ Questions Answer
Q. The magnitude of field flux in a 3-phase synchronous motor
a. remains constant at all loads
b. varies with speed
c. varies with the load
d. varies with power factor
Q. The torque angle, in a synchronous motor, is the angle between
a. the supply voltage and the back e.m.f.
b. magnetising current and back e.m.f.
c. the rotating stator flux and rotor poles
d. none of the above
Q. Hunting in a synchronous motor cannot be due to
a. windage friction
b. variable load
c. variable frequency
d. variable supply voltage
Q. By which of the following methods the constant speed of a synchronous motor can bechanged to new fixed value ?
a. By changing the supply frequency
b. By interchanging any two phases
c. By changing the applied voltage
d. By changing the loa
Q. In a synchronous motor, V-curves represent relation between
a. armature current and field current
b. power factor and speed
c. field current and speed
d. field current and power factor
Q. In a 3-phase, 4-pole, 50 Hz synchronous motor, the frequency, pole number and loadtorque all are halved. The motor speed will be
a. 3000 r.p.m.
b. 1500 r.p.m.
c. 750 r.p.m.
d. none of the above
Q. A synchronous motor connected to infinite bus-bars has at constant full load, 100% excitation and unity power factor. On changing the excitation only, the armature current will have
a. no change of power factor
b. lagging power factor with over-excitation
c. leading power factor with under-excitation
d. leading power factor with over-excitation
Q. Which of the following motors is non-self starting ?
a. D.C. series motor
b. synchronous motor
c. Squirrel cage induction motor
d. Wound round induction motor
Q. In a synchronous motor it the back e.m.f. generated in the armature at noload isapproximately equal to the applied voltage, then
a. the motor is said to be fully loaded
b. the torque generated is maximum
c. the excitation is said to be zero per cent
d. the excitation is said to be hundred per cent
Q. In a synchronous motor, the damping winding is generally used to
a. prevent hunting and provide the starting torque
b. reduce the eddy currents
c. provide starting torque only
d. reduce noise level
Q. If the field of a synchronous motor is underexcited, the power factor will be
a. zero
b. unity
c. lagging
d. leading
Q. The back e.m.f. in the stator of a synchronous motor depends on
a. number of poles
b. flux density
c. rotor speed
d. rotor excitation
Q. The maximum value of torque that a synchronous motor can develop without losingits synchronism, is known as
a. slip torque
b. pull-out torque
c. breaking torque
d. synchronising torque
Q. In a synchronous motor, the armature current has large values for
a. high excitation only
b. low excitation only
c. both high and low excitation
d. none of the above
Q. Which of the following losses, in a synchronous motor, does not vary with load?
a. Windage loss
b. Copper losses
c. Any of the above
d. None of the above