200 Important Synchronous Motor MCQ Question and Answer | PDF Free Download
1.A 3-phsae induction motor draws 1,000 kVA at a pf of 0.8 lag. A synchronous condenser is connected in parallel to draw an additional 750kVA at a power factor of 0.6 led. The pf of the total load supplied by the mains is
- AUnity
- B0.707 lead
- C0.6 lag
- DZero
2.A Synchronous condenser is
- Aa synchronous motor with capacitor connected across terminals to improve pf
- B a synchronous motor operating at full load with leading pf
- CAn overexcited synchronous motor partially supplying mechanical load, and also improving pf of the system to which it is connected
- DAn overexcited synchronous motor operating at no load with leading pf used in large power stations for power factor improvement
3.Which of the following device can be used as phase advancer?
- A3-phase induction motor squirrel cage type
- B3-phase induction motor slip ring type
- CSynchronous motor working at leading power factor
- DSynchronous motor working at lagging power factor
4.The phenomenon of oscillation in of the rotor of a synchronous motor about its equilibrium position corresponding to new load on sudden throwing off or increasing of load is called
- ASwinging
- BCrawling
- CHunting
- DNone of these
5.A 3-phase synchronous motor hunts due to
- AFluctuating load
- BFluctuating supply voltage
- CFaulty connections
- DEither fluctuating load or fluctuating supply voltage
6.In a synchronous motor hunting can be reduced to minimum possible by
- AProviding damper winding in the rotor pole faces
- BUsing a flywheel
- CDesigning the motor for adequate synchronizing power
- DAny of the above methods
7.The damper windings also called the squirrel cage windings or damper girds
- AAre provided in a synchronous motor to make itself starting and to prevent hunting
- BConsists of short-circuited copper bars embedded in the field pole faces of a synchronous motor
- CAre provided on the stator of a synchronous motor for improving the power factor
- DBoth (a) and (b)
8.Damper winding in a synchronous machine is used to
- AHelp in starting as a motor
- BRun it as an induction motor
- CHelp in starting as a motor and to reduce hunting
- DIncrease efficiency
9.During hunting of synchronous motor
- ANegative phase sequence currents are generated
- BHarmonics are developed in the armature circuit
- CDamper bar develops torque
- DField excitation increases
10.When a synchronous motor is running at synchronous speed the damper winding produces
- ADamping torque
- BEddy current torque
- CTorque aiding the developed torque
- DNo torque
11.A pony motor is basically a
- ASmall induction motor
- BDe series motor
- CDc shunt motor
- DDouble winding ac/dc motor
12.The synchronous motor can be started by
- AProviding damper winding in its rotor circuit
- BCoupling it with a dc compound motor
- CCoupling it with a small ac induction motor called the pony motor
- DAny of the above methods
13.The number of poles on a pony motor employ head for starting of a 3-phase synchronous motor should be ____that on the synchronous motor.
- AEqual to
- BMore than
- CLesser than
- DNone of these
14.When a synchronous motor is started, the field winding is energized
- AIn the very beginning
- BWhen the motor attains a speed slightly less than the synchronous speed
- CAfter the motor has attained the synchronous speed and synchronized
- DAny time
15.A 3-phase synchronous motor provided with damper winding is started as a 3-phase
- ASynchronous motor
- BSynchronous alternator
- CInduction motor
- DInduction generator
16.A cylindrical rotor synchronous motor is switched on to the dc supply with its field windings shorted on themselves. it will
- ANot start
- BStart but not run at synchronous speed
- CStart as an induction motor and then run as a synchronous motor
- DStart and run as a synchronous motor
17.If the filed winding of a synchronous motor is short circuited and the motor stator is connected to 3-phase ac supply through an auto transformer, the motor will
- AStart and run as a 3-phase induction motor
- BHunt
- CNot start
- DStart and run as a 3-phase synchronous motor
18.While starting a synchronous motor its field winding should be
- AKept open
- BShort circuited
- CConnected to a dc source
- DNone of the above
19.Synchronous motors are inherently not self-starting motors as
- AThe direction of instantaneous torque on the rotor reverses after each half cycle
- BThere is not slip
- CThe stator dies not produce revolving magnetic field
- DIt has no starting winding
20.Electrical machines (ac) should have proper____ in order to limit the operating temperature
- AVoltage rating
- BCurrent rating
- CSpeed
- DkW rating