Synchronous Motor MCQ Question and Answer
1.Synchronous motors generally have
- ASalient pole rotor
- BSmooth cylindrical rotor
- CEither salient pole or smooth cylindrical rotor
- DNone of the above
2.Number of slip rings in a 3-phase synchronous motor will be
- A0
- B1
- C2
- D3 or 4
3.An ideal synchronous motor has no starting torque because the
- ARotor is made up of salient poles
- BRelative velocity between the stator and the rotor mmfs is zero
- CRelative velocity between the stator and rotor mmfs is not zero
- DRotor winding is highly reactive
4.In a synchronous motor
- AThe rotor mmf and stator mmf are stationary with respect to each other
- BRotor mmf rotates slightly faster in comparison to stator mmf
- CStator mmf rotates slightly faster than rotor mmf
- DNone of the above
5.A synchronous machine is revolving armature and stationary field type Under steady running condition the air gap field
- ARotates ate synchronous speed with respect to stator
- BRotates at synchronous speed in the direction of rotation of rotor
- CRemains stationary with respect to stator
- DRemains stationary with respect to rotor
6.In a synchronous machine, if the armature field axis is ahead of the field flux axis in the direction of rotation the machine operating is
- ASynchronous motor
- BSynchronous generator
- CAsynchronous motor
- DAsynchronous generator
7.In a 3-phase synchronous motor
- ARemains constant at all loads
- BVaries with load
- CVaries with speed
- DVaries with power factor
8.In a 3-phase synchronous motor
- AThe filed mmf leads the air gap flux leads the armature mmf
- BThe armature mmf leads the air gpap flux and air gap flux leads the field mmf
- CThe armature mmf leads the air gap flux and air gap flux lags behind the field mmf
- DNone of the above
9.The relative speed between the magnetic fields of stator and rotor under steady state operation is zero for
- AA dc machines
- BAn induction machine
- CA synchronous machine
- DAll the above machine
10.A 3- phase synchronous motor has
- AHigh starting torque
- BNo starting torque
- CLow starting current
- DLow starting torque
11.A 10 pole, 25Hz alternator is directly coupled to and is driven by 60 Hz synchronous motor. What is the number of poles for the synchronous motor?
- A48
- B12
- C24
- D16
12.A 3- phase synchronous motor needs dc supply for excitation
- AContinuously
- BAt the starting instant only
- COf stator
- DNone of these
13.The armature current of a synchronous motor on no load
- ALeads the applied voltage by 90 degree.
- BLags behind the applied voltage by 90 degree
- CIs in phase will applied voltage
- DZero
14.As the load is increased on a synchronous motor, its speed
- ADecreases
- BIncreases
- CRemains constant and additional load is supplied by shift in relative position no of the rotor with respect to stator rotating magnetic field
- DRemains constant for some time and then falls abruptly
15.The synchronous motor meets increase in load by taking more armature current as
- AThe rotor pole falls back relative to the stator pole causing an increase in motor current
- BThe back emf decreases causing an increase in motor current
- CRotating field is strengthened causing an increase in motor current
- DNone of the above
16.A synchronous motor is operating with normal excitation. With the increase in load the armature current drawn from the supply main increases due to
- AIncrease in back emf
- BFall in motor speed
- CIncrease in resultant voltage across the armature
- DIncrease in power factor
17.The resultant voltage acting across the armature circuit of a synchronous motor (Er) is the _____of induced emf in the armature circuit (Eb) and supply voltage V
- AArithmetic sum
- BArithmetic difference
- CPhasor difference
- DPhasor sum
18.The phase of emf induced in the armature of a synchronous motor (Eb) depends upon
- ARotor speed
- BLoad
- CBoth load and speed
- DNone of the above
19.In a synchronous motor, the synchronizing power come into action when
- ARotor speed either exceeds or falls below the synchronous speed
- BRotor speed is equal to synchronous speeds
- CRotor speed falls below the synchronous speed
- DRotor speed exceeds the synchronous speed
20.The coupling angle or load angle of a synchronous motor is defined as the space angle between the
- ARotor and stator poles of the same polarity
- BRotor and stator poles of opposite polarity
- CRotor and stator teeth
- DNone of the above