Q.1
When the field of a synchronous motor is under-excited, the power factor will be
  • leading
  • lagging
  • unity
  • zero
Q.2
The speed regulation of a synchronous motor is always
  • 1%
  • 0.5%
  • positive
  • zero
Q.3
The percentage slip in case of a synchronous motor is
  • 1%
  • 100%
  • 0.5%
  • zero
Q.4
The operating speed of a synchronous motor can be changed to new fixed value by
  • changing the load
  • changing the supply voltage
  • changing frequency
  • using brakes
Q.5
When load on an over-excited or under excited synchronous*motor is increased, rateof change of its armature current as compared with that of power factor is
  • more
  • less
  • equal
  • twice
Q.6
The rotor copper losses, in a synchronous motor, are met by
  • source
  • armature input
  • motor input
  • supply lines
Q.7
Synchronous motors are
  • not-self starting
  • self-starting
  • essentially self-starting
  • none of the above
Q.8
An over excited synchronous motor is used for
  • fluctuating loads
  • variable speed loads
  • low torque loads
  • power factor corrections
Q.9
The efficiency of a properly designed synchronous motor will usually fall in range
  • 60 to 70%
  • 75 to 80%
  • 85 to 95%
  • 99 to 99.5%
Q.10
Riunting in a synchronous motor takes place
  • when supply voltage fluctuates
  • when load varies
  • when power factor is unity
  • motor is under loaded
Q.11
A three-phase synchronous motor will have
  • no slip-rings
  • one slip-ring
  • two slip-rings
  • three slip-rings
Q.12
In case one phase of a three-phase synchronous motor is short-circuited the motor will
  • not start
  • run at 2/3 of synchronous speed
  • run with excessive vibrations
  • take less than the rated load
Q.13
A synchronous motor can develop synchronous torque
  • when under loaded
  • while over-excited
  • only at synchronous speed
  • below or above synchronous speed
Q.14
A synchronous motor can be started by
  • pony motor
  • compound motor
  • providing damper winding
  • any of the above
Q.15
When V is the applied voltage, then the breakdown torque of a synchronous motorvaries as
  • V
  • V312
  • V2
  • 1/V
Q.16
The back e.m.f. of a synchronous motor depends on
  • speed
  • load
  • load angle
  • all of the above
Q.17
Mostly, synchronous motors are of
  • alternator type machines
  • induction type machines
  • salient pole type machines
  • smooth cylindrical type machines
Q.18
In a synchronous motor which loss varies with load ?
  • Windage loss
  • Bearing friction loss
  • Copper loss
  • Core loss
Q.19
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
Q.20
As the load is applied to a synchronous motor, the motor takes more armature currentbecause
  • the increased load has to take more current
  • the rotor by shifting its phase backward causes motor to take more current
  • the back m.f. decreases causing an increase in motor current
  • the rotor strengthens the rotating field casuing more motor current
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