1. In DC motor, which of the following part can sustain the maximum temperature rise?
Correct : A. field winding
2. Direction of rotation of motor is determined by
Correct : D. fleming’s left-hand rule
3. Which power is mentioned on a name plate of a motor?
Correct : D. output power available at the shaft
4. An electric motor is having constant output power. So, motor will have a torque speed characteristic
Correct : D. rectangular hyperbola
5. The armature shaft of a DC motor must be able to withstand
Correct : D. bending moment, unbalanced magnetic pull and twisting stains
6. In DC machines the residual magnetism is present. The order of residual magnetism is
Correct : A. 2 to 3 per cent
7. How many steps are involved in the construction of single phase induction motor?
Correct : C. 5
8. What kind of motor employs the skein winding made use of?
Correct : B. fractional horse power single phase induction motor
9. A three-point starter is used for
Correct : B. shunt as well as compound motors
10. The starting resistance of a DC shunt motor is generally
Correct : A. low
11. What will happen if DC motor is used without starter?
Correct : A. heavy sparking at brushes
12. In shunt and compound motor starting the shunt field should be made on with full starting resistance in
Correct : C. series with armature
13. A starter is required for a 220-V shunt motor. The maximum allowable current is 55 A and the minimum current is about 35 A. The armature resistance of the motor is 0.4 Ω. What will be the number of sections of starter resistance required?
Correct : C. 6
14. A starting resistance is inserted at the starting in an induction motor as well as dc motor.
Correct : A. induction motor has to control starting torque whereas in dc motor, it is done to avoid large current
15. 2 TYPICAL CONTROL CIRCUITS FOR SHUNT AND SERIES MOTORS
Correct : A. starting resistance would burn
16. The shunt motor starters that can be used is/are
Correct : A. 3-point and 4-point starter
17. Thyristor controlled starter is preferred over DOL starter due to
Correct : A. lesser losses
18. For a 7.46 kW, 200 V dc shunt motor with full load efficiency of 85% has armature resistance of 0.25 ohms. Calculate the value of starting resistance in ohms for a current 1.5 times of the full load current.
Correct : A. 2.788
19. The post effects of the armature reaction is
Correct : D. none of the mentioned
20. If the students give a forward shift of 10° to the dc generator, then it
Correct : A. reduces flux per pole
21. A dc machine is run at rated speed in forward direction and then in backward direction. It is observed that, speeds of the rotation are different, then it leads to the conclusion of
Correct : A. incorrect brush placement
22. For a dc machine, its commutator has a diameter of 50 c rotating at 1000 rpm. For a brush width of 1 cm, the time commutation taken by the machine will be
Correct : A. 0.382 ms
23. An induction motor can be said analogous to
Correct : A. transformer
24. A 3-phase induction motor with its rotor blocked behaves similar to a
Correct : A. transformer under short circuit of secondary terminals
25. The no load current of the transformer is very less due to
Correct : A. mutual flux having low reluctance iron core
26. The no load current of the induction motor is high due to
Correct : A. long and high reluctance path between stator and rotor
27. At no load induction motor has possible power factor as
Correct : A. 0.2
28. Mechanically air gaps in induction motor are kept very low to avoid
Correct : D. all of the mentioned
29. The low no load power factor
Correct : A. reduces full load operating pf
30. An induction motor when started on load, it does not accelerate up to full speed but runs at 1/7th of the rated speed. The motor is said to be
Correct : C. crawling
31. The great advantage of the double squirrel-cage induction motor over single cage rotor is that its
Correct : D. starting current is lower
32. Ward-Leonard system of system of speed control is not recommended for
Correct : A. constant speed operation
33. At a very low speed, increase in field resistance will
Correct : A. decrease the speed of motor
34. Small DC motors have best speed control by
Correct : A. armature voltage control
35. To implement armature voltage control, it must be ensured that
Correct : A. it is used on separately excited machine
36. The torque limit of speed for a shunt motor
Correct : A. remains constant till base speed
37. Run-away for large DC machine is avoided by using
Correct : B. compensating winding
38. Why does DC motor sometimes run too fast when under-loaded?
Correct : A. due to weak field
39. DC machines have windings and synchronous machines use windings.
Correct : A. closed,open
40. The simplex lap winding has the range of winding pitch of
Correct : A. (-2,2)
41. The commutator pitch for a simplex lap winding is equal to
Correct : A. 1 and -1
42. Commutator segments in a DC shunt machine is equal to the number of
Correct : A. coil sides
43. We can employ dummy coils in a DC machine to
Correct : A. compensate reactance voltage
44. In AC machines we should prefer double layer winding over single layer windings because
Correct : A. it requires identical coils
45. While doing regular checks on the dc machine with the lap connected winding, it is reported to have ammeter fluctuations, this can be due to
Correct : D. all of the mentioned
46. A 6-pole lap wound DC generator has a developed power of P watts and brush voltage of E volts. Three adjacent brushes of the machine had been found worn out and got open circuited. If the machine is operated with the remaining brushes, voltage and power that could be obtained from the machine are
Correct : A. e, p
47. 1 = 0.0917.
Correct : A. reduce armature voltage
48. Ward Leonard method is
Correct : C. combination of armature control method and field control method
49. Starting gear used in Ward Leonard method
Correct : D. is absent
50. To get the speed of DC motor below the normal speed without wastage of electrical energy we use
Correct : A. ward leonard control
51. Speed control by Ward Leonard method, can give uniform speed variation
Correct : A. in both directions
52. The disadvantage of the Ward Leonard control method is
Correct : D. high cost, high maintenance and low efficiency
53. 1 SPEED CONTROL OF THREE PHASE INDUCTION MOTOR
Correct : A. slip frequency
54. An 8-pole, 3-phase, 50 Hz induction motor is operating at a speed of 720 rpm. The frequency of the rotor current of the motor in Hz is
Correct : A. 2
55. Calculate the moment of inertia of the disc having a mass of 54 kg and diameter of 91 cm.
Correct : B. 5.589 kgm2
56. In an induction motor, when the number of stator slots is equal to an integral number of rotor slots
Correct : D. the machine may fail to start
57. In the rotor voltage injection method, when an external voltage source is in phase with the main voltage then speed will
Correct : A. increase
58. A 2-pole, 3-phase, Hz induction motor is operating at a speed of 550 rpm. The frequency of the rotor current of the motor in Hz is 2.
Correct : D. 9.37
59. Calculate the average value of the sinusoidal waveform x(t)=848sin(1.65πt+2π÷0.68).
Correct : A. 0
60. In the rotor voltage injection method, when an external voltage source is in opposite phase with the main voltage then speed will
Correct : B. decrease
61. The slip recovery scheme is a part of the synchronous speed changing technique.
Correct : A. true
62. If induction motor air gap power is 1.8 KW and gross developed power is .1 KW, then rotor ohmic loss will be KW.
Correct : A. 1.7
63. Calculate the time period of the waveform v(t)=12sin(8πt+8π÷15)+144sin(2πt+π÷6)+ 445sin(πt+7π÷6).
Correct : B. 4 sec
64. The value of slip at which maximum torque occurs
Correct : A. r2÷x2
65. In AC voltage controllers the
Correct : A. variable ac with fixed frequency is obtained
66. A single-phase half wave voltage controller consists of
Correct : B. one scr is anti parallel with one diode
67. In the below given voltage controller circuit
Correct : B. the negative half cycle at the load is same as the supply vs