OBJECTIVE TYPE QUESTIONS

ELECTRICAL MACHINES – II

1. In an alternator, voltage drops occurs in

(A) armature resistance only

(B) armature resistance and leakage reactance

(C) armature resistance, leakage reactance and armature reaction

(D) armature resistance, leakage reactance, armature reaction and earth connections.

 2. The magnitude of various voltage drops that occur in an alternator, depends on

(A) power factor of the load

(B) load current

(C) power factor x load current

(D) power factor x (load current)².

  

3. In an alternator, at lagging power factor, the generated voltage per phase, as compared to that at unity power factor

(A) must be same as terminal voltage

(B) must be less than the terminal voltage

(C) must be more than the terminal voltage

(D) must be 1.41 time the terminal voltage.

  

4. The power factor of an alternator depends on

(A) Load

(B) Speed of rotor

(C) Core losses

(D) Armature losses.

5. Which kind of rotor is most suitable for turbo alternators which arc designed to run at high speed?

(A) Salient pole type

(B) Non-salient pole type

(C) Both (A) and (B) above

(D) None of the above.

  

6. Salient poles are generally used on

(A) high speed prime movers only

(B) medium speed prime movers only

(C) low speed prime movers only

( D) low and medium speed prime movers.

7. The frequency of voltage generated in an alternator depends on

(A) number of poles

(B) rotating speed

(C) number of poles and  rotating speed

(D) number of poles, rotating speed and type of winding.

 8. The frequency of voltage generated by an alternator having 8 poles and rotating at 250 rpm is

(A) 60 Hz

(B) 50 Hz

(C) 25 Hz

(D) 16 2/3 Hz.

9. An alternator is generating power at 210 V per phase while running at 1500 rpm. If the need of the alternator drops to 1000 rpm, the generated voltage per phase will be

(A) 180 V

(B) 150 V

(C) 140 V

(D) 105 V.

  

10. A 10 pole AC generator rotates at 1200 rpm. The frequency of AC voltage in cycles per second will be

(A)120

(B) 110

(C) 100

(D) 50.

 11. The number of electrical degrees passed through in one revolution of a six pole synchronous alternator is

(A)360^:

(B)720

(C) 1080

(D)2160 .

12. If the input to the prime mover of an alternator is kept constant but the excitation is changed, then the

(A) reactive component of the output is changed

(B) active component of the output is changed

(C) power factor of the load remains constant

(D) power factor of the load reduces.

 13. An alternator is said to be over excited when it is operating at

(A) unity power factor

(B) leading power factor

(C) lagging power factor

(D) lagging to leading power factor.

 14. When an alternator is running on no load the power supplied by the prime mover is mainly consumed

(A) to meet iron losses

(B) to meet copper losses

(C) to meet all no load losses

(D) to produce induced emf in armature winding.

 15.  Machine with negative slip

(A)Induction Motor

(B) Brake

(C)Induction Generator

(D)Synchronous machine

16. When rotor is at standstill

(A)slip is zero

(B)slip is one

(C)Any slip

(D)Slip is infinity

17. In a 3-phase synchronous motor

(A)   the speed of stator MMF is always more than that of rotor MMF.

(B)       the speed of stator MMF is always less than that of rotor MMF.

(C)       the speed of stator MMF is synchronous speed while that of rotor MMF is zero.

(D)      rotor and stator MMF are stationary with respect to each other.

18. The maximum power for a given excitation in a synchronous motor is developed when the power angle is equal to

(A)  0o	(B) 45o
(C) 60o	(D) 90o

19.     A balanced three-phase, 50 Hz voltage is applied to a 3 phase, 4 pole, induction motor. When the motor is delivering rated output, the slip is found to be 0.05. The speed of the rotor m.m.f. relative to the rotor structure is

(A)	1500 r.p.m.	(B)  1425r.p.m.
(C)	25 r.p.m.	(D)  75 r.p.m.

 20. A capacitor start single phase induction motor will usually have a power factor of

(A) unity

(B) 0.8 leading

(C) 0.6 leading

(D) 0.6 lagging.

 21. A capacitor start, capacitor run single phase induction motor is basically a

(A) ac series motor

(B) dc series motor

(C) 2 phase induction motor

(D) 3 phase induction motor.

22. The starting torque of a capacitor start motor is

(A) zero

(B) low

(C) same as rated torque

(D) more than rated torque.

23. The torque developed by a split phase motor is proportional to

(A) Sine of angle between l_m and l_s

(B) Cosine of angle between l_m and I_s

(C) Main winding current, I_m

(D) Auxiliary winding current,I_s

24. A capacitor start single phase induction motor is switched on the supply with its capacitor replaced by an inductor of equivalent reactance value. It will

(A) not start

(B) start and run

(C) start and then stall

(D) none of the above.

 25. The starting capacitor of a single phase motor is

(A) Electrolytic capacitor

(B) Ceramic capacitor

(C) Paper capacitor

(D) None of the above.

26. Which of the following is the most economical method of starting a single phase motor ?

(A) Resistance start method

(B) Inductance start method

(C) Capacitance start method

(D) Split-phase method.

27. The number of turns in the starting winding of a capacitor start motor as compared to that for split phase motor is

(A) same

(B) more

(C) less

(D) none of the above.

28.  In a split phase motor, the ratio of number of turns for starting winding to that for running winding is

(A) 2.0

(B) more than 1

(C) 1.0

(D) less than 1.

29. A single phase motor generally used for small air compressor is

(A) capacitor start capacitor run motor

(B) reluctance motor

(C) universal motor

(D) shaded pole motor.

  

30. Out of the following motors, which will give the highest starting torque ?

(A) Universal motor

(B) Capacitor start motor

(C) Shaded pole motor

(D) All have zero starting torque.

 31. Which single phase ac motor will you select for record players and tape recorders ?

(A) Hysteresis motor

(B) Shaded pole motor

(C) Reluctance motor

(D) Two value capacitor motor.

  

32.  A universal motor is one

(A) which can run on any value of supply voltage

(B) which has infinitely varying speed

(C) which can operate on ac as well as dc voltage

(D) which can work as single phase or three phase motor.

  

33.  Under normal operating conditions which motor can run at 5000 rpm ?

(A) Synchronous motor

(B) Induction motor

(C) Universal motor

(D) No motor can run at 5000 rpm.

  

34. The motor used in household refrigerators is

(A) dc series motor

(B) dc shunt motor

(C) universal motor

(D) single phase induction motor.

 35.Rotor Copper loss is equal to

(A) Friction loss

(B) Stator loss

(C) slip times rotor input

(D) rotational loss

ANSWERS

Electrical Machines – II

Key Answers

1. C                                  33. C                                   

 2. B                                 34. D

 3. C                                 35. C

 4. A                         

 5. B

 6. D

 7. C

 8. D

9. C

10. C

11. C

12. A

13. C

14. C

15. C

16. B

17. D

18. A

19. D

20 .D

 21.C

 22.B

23. A

24. A

25. A

26. C

27. B

28. D

29. A

30. B

31. A

32. C