Synchronous Motors 2

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Objectives for Electrician and Wireman: Synchronous Motors 2

Subject: Synchronous Motors 2

Part 2: Objective questions and answers of Synchronous Motors

 

Q1. An electric motor in which both the rotor and stator fields rotate with the same speed is called……. motor.

a) D.C.

b) Charge

c) Synchronous

d) Universal

 

Q2. If the field of a synchronous motor is under excited, the power factor will be

a) Lagging

b) Leading

c) Unity

d) More than unity

 

Q3. Synchronous capacitor is

a) An ordinary static capacitor bank

b) An over-excited synchronous motor driving mechanical load

c) Over excited synchronous motor running without mechanical load

d) None of the above

 

Q4. The direction of rotation of a synchronous motor can be reversed by reversing

a) Current to the field winding

b) Supply phase sequence

c) Polarity of rotor poles

d) None of the above

 

Q5. In a synchronous motor, damper winding is provided in order to

a) Stabilize rotor motion

b) Suppress rotor oscillations

c) Develop necessary starting torque

d) Both "b" and "c"

 

Q6. The v-curves of a synchronous motor show relationship between

a) Excitation current and back e.m.f.

b) Field current and power factor

c) D.C. field current and A.C. armature current

d) Armature current and supply voltage

 

Q7. The angle between the synchronously rotating stator flux and rotor poles of a synchronous motor is called……. Angle

a) Synchronizing

b) Torque

c) Power factor

d) Slip

 

Q8. The motor whose rotor and rotating magnetic field of the stator rotate at the same speed is called:

a) Induction motor

b) Slip-ring induction motor

c) Synchronous motor

d) Universal motor

 

Q9. Which one of the following characteristic is not applicable to synchronous motors?

a) Runs at constant speed at all loads

b) Suitable to supply only mechanical load

c) Can also be used for pf improvement

d) Not self-starting

 

Q10. Which one of the following is the application of synchronous motor?

a) Cranes

b) Hoists

c) Power factor correction device

d) Welding generator set

 

Q11. Why d.c supply is necessary for synchronous motor operation?

a) Reduce the losses

b) Start the motor initially

c) Run the motor with over load

d) Run the motor at synchronous speed

 

Q12. What is the function of inverter?

a) Convert a.c to d.c

b) Convert d.c to a.c

c) Smoothening a.c sine wave

d) Convert pulsating dc into pure d.c

 

Q13. Why exciter is essential to run a synchronous motor?

a) Carry more load in motor

b) Improve the power factor

c) Reduce the losses in motor

d) Run the motor at synchronous speed

 

Q14. Why the LED's are avoided as converters in rectifier diodes?

a) Heavily doped device

b) Very low power device

c) Designed for light emitting

d) Very sensitive to temperature

 

Q15. What is the advantage of motor generator set?

a) Noiseless

b) High efficiency

c) Low maintenance required

d) Dc output voltage can be easily controlled

 

Q16. Why the synchronous motor fails to run at synchronous speed?

a) Insufficient excitation

b) Defective pony motor

c) Open in damper winding

d) Short in damper

 

Q17. What is the function of damper windings in synchronous motor?

a) Maintain power factor

b) Excite the field winding

c) Maintain constant speed

d) Start the synchronous motor

 

Q18. How synchronous motor works as a power factor corrector?

a) Varying the line voltage

b) Varying the field excitation

c) Increasing the speed of motor

d) Decreasing the speed of motor

 

Q19. The no. Of poles of a 3-phase induction motor running at 500 r.p.m. will be: (supply frequency = 50 Hz)

a) 12

b) 76

c) 4

d) 2

 

Q20. At the time of starting, the slip of an induction-motor is equal to:

a) Infinite

b) Unit

c) Zero

d) None of these

 

Part 2: Objective questions and answers of Synchronous Motors

 

Q1. Answer c

 

Q2. Answer a

 

Q3. Answer b

 

Q4. Answer b

 

Q5. Answer d

 

Q6. Answer c

 

Q7. Answer b

 

Q8. Answer c

 

Q9. Answer b

 

Q10. Answer c

 

Q11. Answer d

 

Q12. Answer b

 

Q13. Answer d

 

Q14. Answer b

 

Q15. Answer d

 

Q16. Answer a

 

Q17. Answer d

 

Q18. Answer b

 

Q19. Answer a

 

Q20. Answer b

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