Top 80+ Solved 3 Phase Induction Motors MCQ Questions Answer
Q. An induction motor can run at synchronous speed when
a. it is run on load
b. it is run in reverse direction
c. it is run on voltage higher than the rated voltage
d. e.m.f. is injected in the rotor circuit
Q. Which motor is preferred for use in mines where explosive gases exist ?
a. Air motor
b. Induction motor
c. D.C. shunt motor
d. Synchronous motor
Q. The torque developed by a 3-phase induction motor least depends on
a. rotor current
b. rotor power factor
c. rotor e.m.f.
d. shaft diameter
Q. In an induction motor if air-gap is increased
a. the power factor will be low
b. windage losses will be more
c. bearing friction will reduce
d. copper loss will reduce In an induction motor
Q. In induction motor, percentage slip depends on
a. supply frequency
b. supply voltage
c. copper losses in motor
d. none of the above
Q. When /?2 is tne rotor resistance, .X2 the rotor reactance at supply frequency and s the slip, then the condition for maximum torque under running condi-tions will be
a. sR2X2 = 1
b. sR2 = X2
c. R2 = sX2 i
d. R2 = s2X2
Q. In case of a double cage induction motor, the inner cage has
a. high inductance arid low resistance
b. low inductance and high resistance
c. low inductance and low resistance
d. high inductance and high resis¬tance
Q. The low power factor of induction motor is due to
a. rotor leakage reactance
b. stator reactance
c. the reactive lagging magnetizing current necessary to generate the magnetic flux
d. all of the above
Q. Insertion of reactance in the rotor circuit
a. reduces starting torque as well as maximum torque
b. increases starting torque as well as maximum torque
c. increases starting torque but maxi-mum torque remains unchanged
d. increases starting torque but maxi-mum torque decreases
Q. Insertion of resistance in the rotcir of an induction motor to develop a given torque
a. decreases the rotor current
b. increases the rotor current
c. rotor current becomes zero
d. rotor current rernains same
Q. For driving high inertia loods best type of induction motor suggested is
a. slip ring type
b. squirrel cage type
c. any of the above
d. none of the above
Q. Temperature of the stator winding of a three phase induction motor is obtained by
a. resistance rise method
b. thermometer method
c. embedded temperature method
d. all above methods
Q. The purpose of using short-circuit gear is
a. to short circuit the rotor at slip rings
b. to short circuit the starting resis¬tances in the starter
c. to short circuit the stator phase of motor to form star
d. none of the above
Q. In a squirrel cage motor the induced e.m.f. is
a. dependent on the shaft loading
b. dependent on the number of slots
c. slip times the stand still e.m.f. induced in the rotor
d. none of the above