Single Phase Motors - Multiple Choice Questions

Single Phase Motors - Multiple Choice Questions Points : single phase motors, multiple choice questions and answers, electrical objective type question answers, mcqs

1. The full-load efficiency of a shaded pole motor is about ……………

   (i) 70 to 80%

   (ii) 60 to 70%

   (iii) 30 to 35%

   (iv) 5 to 10%

2. A vacuum cleaner employs motor.

   (i) resistance split-phase

   (ii) capacitor-start

   (iii) shaded-pole motor

   (iv) single-phase series motor

3. The direction of split-phase induction motor can be reversed by interchanging the connections of supply of ............

   (i) either main or starting winding

   (ii) both main and starting winding

   (iii) rotor winding

   (iv) none of the above

4. For the same rating, the efficiency of a single-phase induction motor is .............. that of 3-phase induction motor.

   (i) less than

   (ii) the same as

   (iii) more than

   (iv) none of the above

5. Most of single-phase induction motors are …………. machines.

   (i) 2-pole

   (ii) 6-pole

   (iii) 8-pole

   (iv) 4-pole

6. The main winding and starting winding of a single-phase induction motor are connected in ............ across the supply.

   (i) series

   (ii) parallel

   (iii) series-parallel

   (iv) none of the above

7. The starting winding of a single-phase induction motor has ............... that of main winding.

   (i) more poles than

   (ii) less poles than

   (iii) same number of poles as

   (iv) none of the above

8. A 50 Hz, 4-pole single phase motor will have a synchronous speed of

   (i) 1500 r.p.m

   (ii) 750 r.p.m

   (iii) 1200 r.p.m

   (iv) none of the above

9. A 1/3 H.P., 120V, 60 Hz capacitor-start motor has the following constants for the main and starting windings:
   Main winding : Z_m = (4.5 + j 3.7) ohms
   Starting winding : Z_s = (9.5 + j 3.5) ohms
   The value of starting capacitance that will place the main and starting winding currents in quadrature at starting is

   (i) 212 µF

   (ii) 177 µF

   (iii) 315 µF

   (iv) 424 µF

10. The direction of rotation of shaded-pole motor depends upon ..............

    (i) supply frequency

    (ii) number of poles on the stator

    (iii) which half of the pole is shaded

    (iv) supply voltage

11. In a single-phase induction motor, speed-sensitive centrifugal switch is connected in …………. winding.

    (i) parallel with main

    (ii) series with main

    (iii) series with starting

    (iv) parallel with starting

12. A 4-pole, 50 Hz single-phase induction motor is running with a slip of 3.4%. The speed of the motor is

    (i) 1279 r.p.m.

    (ii) 1120 r.p.m.

    (iii) 1449 r.p.m.

    (iv) 1540 r.p.m.

13. If I_m and I_s are the currents in the main and starting windings respectively and α is the angle between I_m and I_s then motor torque T is given by ……………

    (i) T α I_m I_s cos α

    (ii) T α I_m I_s sin α

    (iii) T α I_m I_s

    (iv) none of the above

14. Which of the following single-phase motor is available with speed as low as one revolution per month?

    (i) shaded-pole

    (ii) reluctance

    (iii) hysteresis

    (iv) universal

15. The purpose of starting winding in a single-phase induction motor is to ..............

    (i) reduce losses

    (ii) limit temperature rise of the machine

    (iii) produce rotating flux in conjunction with main winding

    (iv) none of the above

16. The resistance split-phase induction motor has starting torque.

    (i) high

    (ii) moderate

    (iii) very low

    (iv) none of the above

17. The resistance split-phase induction motors are the most popular single-phase motors because of …………..

    (i) their low cost

    (ii) their high starting torque

    (iii) the long starting period

    (iv) none of the above

18. In a capacitor-start, capacitor-run motor, winding is cut out after starting.

    (i) starting

    (ii) main

    (iii) neither starting nor main

    (iv) none of the above

19. At starting, the winding of a 220V, 50 Hz split-phase induction motor have the following values:
    Main winding : R = 10 Ω ; X_L = 25 Ω
    Starting winding : R = 25 Ω ; X_L = 15 Ω
    What is the power factor of the motor?

    (i) 0.85 lag

    (ii) 0.64 lag

    (iii) 0.52 lag

    (iv) 0.707 lag

20. For the same rating, the p.f. of a single-phase induction motor is ............... that of 3-phase induction motor.

    (i) the same as

    (ii) less than

    (iii) more than

    (iv) none of the above

21. A capacitor-start, capacitor-run motor has ...........

    (i) low power factor

    (ii) high power factor

    (iii) low efficiency

    (iv) high starting torque

22. The capacitor-start, capacitor-run induction motor acts as a true 2-phase motor at …………

    (i) starting

    (ii) no load

    (iii) all loads

    (iv) full-load

23. The capacitor-start, capacitor-run motor is used in those applications where

    (i) high starting torque is required

    (ii) silence is important

    (iii) noisy operation is not important

    (iv) none of the above

24. The capacitor-start, capacitor-run motor has ………..

    (i) no centrifugal switch

    (ii) low power factor

    (iii) noisy operation

    (iv) low efficiency

25. Capacitor motors .............. resistance split-phase induction motors.

    (i) are costlier than

    (ii) are less costly than

    (iii) cost about the same as

    (iv) poor starting torque than

26. Most of the troubles of single phase induction motors are traceable to the............,....

    (i) rotor bars

    (ii) main winding

    (iii) shaft bearings

    (iv) starting switch

27. The single phase shaded pole motor has …………….

    (i) squirrel cage rotor

    (ii) wound rotor

    (iii) high power factor

    (iv) high starting torque

28. The resistance split-phase induction motor is used in those applications where …………

    (i) starting is frequent

    (ii) starting period is long

    (iii) starting is infrequent

    (iv) none of the above

29. A 4-pole, 50 Hz single-phase induction motor has a slip of 5 %. The speed of the motor will be ……………….

    (i) 1500 r.p.m

    (ii) 1425 r.p.m

    (iii) 1200 r.p.m

    (iv) none of the above

30. At starting, the line current of a capacitor-start induction motor is ............... the normal full-load current.

    (i) 8 to 10 times

    (ii) 4 to 5 times

    (iii) equal to

    (iv) 7 to 8 times

31. The single phase series motor can operate on …………….

    (i) a.c. only

    (ii) d.c. only

    (iii) both a.c. and d.c

    (iv) none of the above

32. For the same rating, a d.c. series motor costs single phase series motor.

    (i) about the same as

    (ii) more than

    (iii) less than

    (iv) none of the above

33. A 2 H.P. d.c. series motor will weigh 2 H.P. single phase series motor.

    (i) about the same as

    (ii) less than

    (iii) more than

    (iv) none of the above

34. The best suited motor to drive 1/4 H.P. fan in a hospital ward would be ................ motor.

    (i) shaded-pole

    (ii) single-phase series motor

    (iii) capacitor-run motor

    (iv) hysteresis motor

35. The washing machine generally employs ………. motor.

    (i) single-phase series motor

    (ii) resistance split-phase

    (iii) shaded-pole

    (iv) hysteresis

36. The best suited motor to drive 3/4 H.P. air compressor would be ............... motor.

    (i) capacitor-start

    (ii) single-phase series

    (iii) shaded-pole

    (iv) resistance split-phase

37. A single-phase induction motor employs rotor.

    (i) squirrel cage

    (ii) wound

    (iii) either squirrel cage or wound

    (iv) none of the above

38. The least expensive fractional horse power motor is ............. motor.

    (i) shaded-pole

    (ii) capacitor-start

    (iii) split-phase

    (iv) a.c. series

39. A 4-pole, 250 W, 115 V, 60 Hz capacitor start induction motor takes a full-load line current of 5.3A while running at 1760 r.p.m. The full-load efficiency of the motor is 64%.
    The slip is

    (i) 4.3%

    (ii) 1.8%

    (iii) 8.3 %

    (iv) 2.2 %

40. A 4-pole, 250 W, 115 V, 60 Hz capacitor start induction motor takes a full-load line current of 5.3A while running at 1760 r.p.m. The full-load efficiency of the motor is 64%.
    The motor power factor is

    (i) 0.64 lag

    (ii) 0.32 lag

    (iii) 0.707 lag

    (iv) 0.85 lag

41. A 4-pole, 250 W, 115 V, 60 Hz capacitor start induction motor takes a full-load line current of 5.3A while running at 1760 r.p.m. The full-load efficiency of the motor is 64%.
    The full-load torque is

    (i) 2.6 N-m

    (ii) 1.35 N-m

    (iii) 4.5 N-m

    (iv) 7.8 N-m

42. A 200 W, 230 V, 50 Hz capacitor-start motor has the following winding parameters:
    Main winding : R = 4.5 Ω ; X_L = 3.7 Ω
    Starting winding : R = 9.5 Ω ; X_L = 3.5 Ω
    What should be the angle between input voltage and starting winding current to give maximum starting torque?

    (i) 38.2ᵒ

    (ii) 24.6ᵒ

    (iii) 50.4ᵒ

    (iv) 32.7ᵒ

43. A 200 W, 230 V, 50 Hz capacitor-start motor has the following winding parameters:
    Main winding : R = 4.5 Ω ; X_L = 3.7 Ω
    Starting winding : R = 9.5 Ω ; X_L = 3.5 Ω
    What should be the capacitance of the starting capacitor that will result n the maximum starting torque?

    (i) 104 µF

    (ii) 189 µF

    (iii) 304 µF

    (iv) 212 µF

44. The nameplate of a 1-phase, 4-pole induction motor gives the following data:
    Output 373W ; 230V, Frequency 50 Hz ; Input current 2.9A Power factor 0.71 ; speed 1410 r.p.m. The full-load slip of the motor is

    (i) 6%

    (ii) 2%

    (iii) 4 %

    (iv) 3 %

45. For the same rating, the size of a single-phase induction motor is about .............. that of the corresponding 3-phase induction motor.

    (i) 3 times

    (ii) the same as

    (iii) 1.5 times

    (iv) 0.33 times

46. The nameplate of a 1-phase, 4-pole induction motor gives the following data:
    Output 373W ; 230V, Frequency 50 Hz ; Input current 2.9A Power factor 0.71 ; speed 1410 r.p.m. what is the efficiency of the motor?

    (i) 65.3%

    (ii) 78.7%

    (iii) 89.2%

    (iv) 70.6%

47. At starting, the winding of a 220V, 50 Hz split-phase induction motor have the following values:
    Main winding : R = 10 Ω ; X_L = 25 Ω
    Starting winding : R = 25 Ω ; X_L = 15 Ω
    What is the phase angle between I_m and I_s?

    (i) 21.2ᵒ

    (ii) 49.4ᵒ

    (iii) 37.7ᵒ

    (iv) 32.6ᵒ

48. At starting, the winding of a 220V, 50 Hz split-phase induction motor have the following values:
    Main winding : R = 10 Ω ; X_L = 25 Ω
    Starting winding : R = 25 Ω ; X_L = 15 Ω
    What is the starting torque if k = 0.53?

    (i) 15 N-m

    (ii) 31 N-m

    (iii) 20 N-m

    (iv) 48 N-m

49. At starting, the winding of a 220V, 50 Hz split-phase induction motor have the following values:
    Main winding : R = 10 Ω ; X_L = 25 Ω
    Starting winding : R = 25 Ω ; X_L = 15 Ω
    What is the line current?

    (i) 14.9 A

    (ii) 8.7 A

    (iii) 21.2A

    (iv) 13.7 A

50. At starting, the winding of a 220V, 50 Hz split-phase induction motor have the following values:
    Main winding : R = 10 Ω ; X_L = 25 Ω
    Starting winding : R = 25 Ω ; X_L = 15 Ω
    A 160 µF capacitor is connected in series with the starting winding of the motor. The phase displacement between I_m , and I_s is?

    (i) 41.5ᵒ

    (ii) 83.7ᵒ

    (iii) 79.2ᵒ

    (iv) 64.5ᵒ

51. At starting, the winding of a 220V, 50 Hz split-phase induction motor have the following values:
    Main winding : R = 10 Ω ; X_L = 25 Ω
    Starting winding : R = 25 Ω ; X_L = 15 Ω
    A 160 µF capacitor is connected in series with the starting winding of the motor.
    What will be the value of starting torque?

    (i) 36.7 N-m

    (ii) 19.8 N-m

    (iii) 24.5 N-m

    (iv) 41.2 N-m

52. A single-phase induction motor runs normally at 1125 r.p.m. on 60 Hz power supply. How many poles must it have?

    (i) 8

    (ii) 6

    (iii) 4

    (iv) 2

53. A single phase motor runs normally at 183 rad/sec on 60 Hz power supply. How many poles must it have?

    (i) 10

    (ii) 8

    (iii) 12

    (iv) 4

54. A 250 W resistance split-phase induction motor has the following currents in the various windings at the moment of starting:
    Main winding current, I_m = 9 A at ф_m = 40.5ᵒ lag
    Starting winding current, I_s , = 6A at ф_s = 15.5ᵒ lag
    What is the component of the 4 in phase with the line voltage?

    (i) 6.844 A

    (ii) 3.862 A

    (iii) 8.626 A

    (iv) none of the above

55. A 250 W resistance split-phase induction motor has the following currents in the various windings at the moment of starting:
    Main winding current, I_m = 9 A at ф_m = 40.5ᵒ lag
    Starting winding current, I_s , = 6A at ф_s = 15.5ᵒ lag
    What is the quadrature component of starting winding current?

    (i) −2.51A

    (ii) −1.603A

    (iii) −3.525A

    (iv) none of the above

56. In a split-phase inductor motor, the two stator windings

    (i) have equal R/X_L ratio

    (ii) are mutually displaced by 90ᵒ electrical

    (iii) draw only the in-phase currents

    (iv) draw equal currents

57. As compared to capacitor-start induction motors or split-phase motors, a permanent-split capacitor motor has lower

    (i) efficiency

    (ii) cost

    (iii) noise

    (iv) power-factor

58. A resistance split-phase induction motor is used for

    (i) low inertia loads

    (ii) high inertia loads

    (iii) very high inertia loads

    (iv) none of the above