Q.1
The frame of an induction motor is usually made of
  • silicon steel
  • cast iron
  • aluminium
  • bronze
Q.2
Rotor rheostat control method of speed control is used for
  • squirrel-cage induction motors only
  • slip ring induction motors only
  • both (a) and (b)
  • none of the above
Q.3
Which of the following component is usually fabricated out of silicon steel ?
  • Bearings
  • Shaft
  • Statorcore
  • None of the above
Q.4
A 3-phaseV,Hz induction motor hasslip. The frequency of rotor e.m.f. willbe
  • 200 Hz
  • 50 Hz
  • 2 Hz
  • 0.2 Hz
Q.5
In case of 3-phase induction motors, plugging means
  • pulling the motor directly on line without a starter
  • locking of rotor due to harmonics
  • starting the motor on load which is more than the rated load
  • interchanging two supply phases for quick stopping
Q.6
If a 3-phase supply is given to the stator and rotor is short circuited rotor will move
  • in the opposite direction as the direction of the rotating field
  • in the same direction as the direction of the field
  • in any direction depending upon phase squence of supply
  • none
Q.7
The speed characteristics of an induction motor closely resemble the speedloadcharacteristics of which of the following machines
  • series motor
  • shunt motor
  • universal motor
  • none of the above
Q.8
Which type of bearing is provided in small induction motors to support the rotor shaft?
  • Ball bearings
  • Cast iron bearings
  • Bush bearings
  • None of the above
Q.9
5 H.P., 50-Hz, 3-phase,V, induction motors are available for the following r.p.m.Which motor will be the costliest ?
  • 730 r.p.m.
  • 960 r.p.m.
  • 1440 r.p.m.
  • 2880 r.p.m.
Q.10
Which is of the following data is required to draw the circle diagram for an inductionmotor ?
  • Block rotor test only
  • No load test only
  • Block rotor test and no-load test
  • Block rotor test, no-load test and stator resistance test
Q.11
The vafcie of transformation ratio of an induction motor can be found by
  • open-circuit test only
  • short-circuit test only
  • stator resistance test
  • none of the above
Q.12
The power scale of circle diagram of an induction motor can be found from
  • stator resistance test
  • no-load test only
  • short-circuit test only
  • noue of the above
Q.13
In induction motor, percentage slip depends on
  • supply frequency
  • supply voltage
  • copper losses in motor
  • none of the above
Q.14
The low power factor of induction motor is due to
  • rotor leakage reactance
  • stator reactance
  • the reactive lagging magnetizing current necessary to generate the magnetic flux
  • all of the above
Q.15
Temperature of the stator winding of a three phase induction motor is obtained by
  • resistance rise method
  • thermometer method
  • embedded temperature method
  • all above methods
Q.16
The starting torque of a three phase induction motor can be increased by
  • increasing slip
  • increasing current
  • both (a) and (b)
  • none of the above
Q.17
The circle diagram for an induction motor cannot be used to determine
  • efficiency
  • power factor
  • frequency
  • output
Q.18
Blocked rotor test on induction motors is used to find out
  • leakage reactance
  • power factor on short circuit
  • short-circuit current under rated voltage
  • all of the above
Q.19
Which motor is preferred for use in mines where explosive gases exist ?
  • Air motor
  • Induction motor
  • shunt motor
  • Synchronous motor
Q.20
The efficiency of an induction motor can be expected to be nearly
  • 60 to 90%
  • 80 to 90%
  • 95 to 98%
  • 99%
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