Q.1
A synchronous motor develops maximum power when load angle is
  • 45°
  • 60°
  • 90°
  • 120°
Q.2
If the synchronous motor, properly synchronised to the supply is running on no load and is having negligible loss then
  • the stator current will be zero
  • the stator current will be very small
  • the stator current will be very high
  • the back m.f. will be more than the supply voltage
Q.3
For power factor correction, synchronous motors operate at
  • no-load and greatly over-excited fields
  • no-load and under-excited fields
  • normal load with minimum excitation
  • normal load with zero excitation
Q.4
The construction of a synchronous motor resembles
  • a series motor
  • an induction motor
  • an alternator
  • a rotary converter
Q.5
A synchronous machine with low value of short-circuit ratio has
  • lower stability limit
  • high stability limit
  • good speed regulation
  • good voltage regulation
Q.6
The duration of sudden snort-circuit test on a synchronous motor is usually about
  • one hour
  • one minute
  • one second
  • none of the above
Q.7
The size of a synchronous motor decreases with the increase in
  • flux density
  • horse power rating
  • speed
  • all of the above
Q.8
The back e.m.f. in the stator of a synchronous motor depends on
  • number of poles
  • flux density
  • rotor speed
  • rotor excitation
Q.9
If the field of a synchronous motor is underexcited, the power factor will be
  • zero
  • unity
  • lagging
  • leading
Q.10
In a synchronous motor it the back e.m.f. generated in the armature at noload isapproximately 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
Q.11
A synchronous motor connected to infinite bus-bars has at constant full load,excitation and unity power factor. On changing the excitation only, the armature current will have
  • no change of power factor
  • lagging power factor with over-excitation
  • leading power factor with under-excitation
  • leading power factor with over-excitation
Q.12
By which of the following methods the constant speed of a synchronous motor can bechanged to new fixed value ?
  • By changing the supply frequency
  • By interchanging any two phases
  • By changing the applied voltage
  • By changing the loa
Q.13
Hunting in a synchronous motor cannot be due to
  • windage friction
  • variable load
  • variable frequency
  • variable supply voltage
Q.14
The magnitude of field flux in a 3-phase synchronous motor
  • remains constant at all loads
  • varies with speed
  • varies with the load
  • varies with power factor
Q.15
The ratio of starting torque to running torque in a synchronous motor is
  • zero
  • one
  • two
  • infinity
Q.16
The net armature voltage of a synchronous motor is equal to the
  • vector sum of Eb and V
  • arithmetic sum of Eb and V
  • arithmetic difference of Eb and V
  • vector difference of Eh and V
Q.17
The induced e.m.f. in a synchronous motor working on leading power factor will be
  • more than the supply voltage
  • less than the supply voltage
  • equal to the supply voltage
  • none
Q.18
In a 3-phase synchronous motor, the negative phase sequence exists when the motor is
  • supplied with unbalanced voltage
  • under-loaded
  • over-loaded
  • none of the above
Q.19
In a synchronous motor, the maximum power developed depends on all of the following except
  • rotor excitation
  • maximum value of coupling angle
  • direction of rotation
  • supply voltage
Q.20
The maximum speed variation in a 3-phase synchronous motor is
  • 10 per cent
  • 6 per cent
  • 4 per cent
  • zero
Q.21
If the field circuit of an unloaded salientpole synchronous motor gets suddenly open- circuited, then
  • it runs at a slower speed
  • the motor stops
  • it continues to run at the same speed
  • it runs at a very high speed
Q.22
If one-phase of a 3-phase synchronous motor is short-circuited, motor
  • will refuse to start
  • will overheat in spots
  • will not come upto speed
  • will fail to pull into step
Q.23
The power factor of a synchronous motor is better than that of induction motor because
  • stator supply is relieved of responsibility of producing magnetic field
  • mechanical load on the motor can be adjusted
  • synchronous motor runs at synchronous speed
  • synchronous motor has large air gap
Q.24
While starting a salient pole synchronous motor by induction motor action and connecting field discharge resistance across field, starting and accelerting torque is produced by
  • induction motor torque in field winding
  • induction motor torque in damper winding
  • eddy current and hysteresis torque in pole faces
  • all of the above methods
Q.25
Change of D.C. excitation of a synchronous motor changes
  • applied voltage of the motor
  • motor speed
  • power factor of power drawn by the motor
  • any of the above
Q.26
An important advantage of a synchronous motor over wound round induction motoris that
  • its power factor may be varied at will
  • its speed is independent of supply frequency
  • its speed may be controlled more easily
  • none of the above
Q.27
A synchronous machine with large air gap has
  • a higher value of stability limit
  • a small value of inherent regulation
  • a higher synchronizing power which makes the machine less sensitive to load variations
  • all of the above
Q.28
The standard full-load power factor ratings for synchronous motors are
  • zero or 0.8 leading
  • unity or 0.8 lagging
  • unity or 0.8 leading
  • unity or zero
Q.29
A synchronous motor can be made self starting by providing
  • damper winding on rotor poles
  • damper winding on stator
  • damper winding on stator as well as rotor poles
  • none of the above
Q.30
The shaft of synchronous motor is made of
  • mild steel
  • chrome steel
  • alnico
  • stainless steel
0 h : 0 m : 1 s