200 Important Synchronous Motor MCQ Question and Answer | PDF Free Download
1.The value of load angle for a synchronous motor depends mainly upon its
- AExcitation
- BLoad
- CSpeed
- DSupply voltage
2.The total steady state torque to drive the synchronous motor and the load at synchronous speed is known as ______ torque.
- AReluctance
- BPull-out
- CSynchronous
- DAverage
3.Electromagnetic torque is present in rotating machines when
- AStator winding carried current
- BRotor winding carried current
- CBoth stator and rotor windings carry current
- DNone of the above
4.In a synchronous motor electromagnetic power varies
- ADirectly as applied voltage
- BDirectly as square of the applied voltage
- CInversely as applied voltage
- DNone of the above
5.The interaction torque in a synchronous motor depends upon
- AStator field strength alone
- BRotor field strength alone
- CTorque angle alone
- DAll of the above i.e. on stator field and rotor field strengths and torque angle
6.A synchronous motor is supplying a load at unity pf. If the load on the motor is increased keeping its excitation and terminal voltage constant, the power factor
- AWill remain the same
- BWill become leading
- CWill become lagging
- DNone of the above
7.When does a synchronous motor operate with leading power factor current?
- AWhile it is under excited
- BWhile it is critically excited
- CWhile it is overexcited
- DWhile it is heavily loaded
8.A 3-phase induction motor connected to an infinite bus is operating at half full load with normal excitation. When the load on the synchronous motor is suddenly increased
- AIts speed will first decrease and then become synchronous
- BIts speed will first increase and then become synchronous
- CIts speed will fluctuate around synchronous speed and then become synchronous
- DIts speed will remain unchanged
9.What is the effect of the field failure of salient pole synchronous motor connected with infinite bus?
- AReduce motor torque and speed
- BNot charge motor torque and speed
- CStop the motor
- DReduce motor torque but motor will continue to run at synchronous speed
10.A salient pole synchronous motor continues running even if its excitation current is reduced to zero. This is due to
- ARotating magnetic field of stator
- BRotating magnetic field of rotor
- CMagnetization of rotor salient poles by stator magnetic field
- DInter looking action between stator and rotor rotating magnetic fields
11.When the excitation of normally operating unloaded salient pole synchronous motor suddenly gets disconnected, it continues to run as a
- ACharge motor
- BSpherical motor
- CSwitched reluctance motor
- DVariable reluctance motor
12.A salient pole synchronous motor is running on no load. If its excitation is made off, it will
- AContinue running at synchronous speed
- BContinue running but at a speed slightly less than synchronous one
- CStop
- DNone of these
13.A synchronous machine connected to a power system, grid bus-bar is operating as a generator. To make the machine operate as a motor the
- ADirection of rotation is to be reversed
- BPhase sequence is to be changed
- CField excitation is to be decreased
- DMechanical input is to be less than the losses at the shaft
14.A synchronous generator connected to an infinite bus is over excited. Considering only, the reactive power, from the point of view of the system the machine acts as
- ACapacitor
- BInductor
- CResistor
- DNone of the above
15.A three-phase synchronous motor connected to ac mains is running at full load and unity power factor. If its shaft load is reduced by half, with field current held constant, its new power factor will be
- AUnity
- BLeading
- CLagging
- DDepend on machine parameters.
16.In a synchronous machine if the axis of the filed flux coincides with that of armature flux, the machine
- AWill operate smoothly without any vibration
- BIs said to be floating
- CIs operating as a synchronous generator
- DIs operating as a synchronous motor
17.A smooth cylindrical synchronous motor will always stop when
- AExcitation winding gets disconnected
- BLoad varies
- CSupply voltage fluctuates
- DSupply frequency varies
18.The speed of a synchronous motor can be varied by varying its
- AExcitation
- BSupply voltage
- CSupply frequency
- DLoad
19.For a 3-phase, 4-pole, 50 Hz synchronous motor the frequency, pole number and the load torque are all halved. The motor speed will be
- A375 rpm
- B75 rpm
- C1,500 rpm
- D3,000 rpm
20.A synchronous motor with comparatively large air gap gives
- AHigher stability limit
- BHigher synchronizing power making the machine less sensitive to load variations
- CBoth (a) and (b)
- DNone of these