2. A high starting torque is offered by the Belt Conveyors.
Correct : A. true
3. Which starting method is the worst method in Induction motor?
Correct : C. reactance starting
4. Explanation: Intermittent duty cycle has frequent on load and off-loads period. The on-load period and off-loads periods are too
Correct : A. frequency changer
5. The capacity of the Crane is expressed in terms of tonnes.
Correct : A. true
6. 1800 second rated motors are used for
Correct : C. medium duty cranes
7. Calculate the frequency of the rotor side of the IM if the value of slip is 0.34 and the supply frequency is 70 Hz.
Correct : A. 23.8 hz
8. frequency is 2 Hz.
Correct : A. 50 hz
9. values of the capacitor and inductor are 4 F and 4 H.
Correct : A. .25 rad/sec
10. Calculate the value of the angular acceleration of the Heavy duty crane using the given data: J = 5 kg-m2, load torque = 30 N-m, motor torque = 80 N-m.
Correct : A. 10 rad/s2
11. motor torque = 2 N-m.
Correct : B. the machine will fail to start
12. The direction of the single-phase IM can be reversed by using which one of the method?
Correct : A. by interchanging the supply terminals
13. Which motor is preferred for overhead traveling cranes?
Correct : A. intermittent periodic motor
14. conditions where electric motors are being used?
Correct : A. thermography
15. What is the range of size of the motor (kW) for efficiency nearly equals to 90%?
Correct : A. 15-150
16. Calculate the heat loss in the electric motor for time interval 0-5 sec using the following data: Ia=2 A, Ra=.8Ω.
Correct : A. 16 j-sec
17. sec.
Correct : C. .293
18. Overloading can be prevented using
Correct : A. over-current protection
19. Full form of IDMT is
Correct : A. inverse definite minimum time
20. The most common cause of motor failure is
Correct : B. low resistance
21. Full form of THD is
Correct : C. total harmonic distortion
22. Calculate the compensator rating required for a sec(Φ)=1.
Correct : D. 0 p.u
23. Calculate the value of Voltage ripple factor if the Form factor is 1.1.
Correct : A. 45.8 %
24. Calculate the value of THD if the
Correct : B. 75 %
25. Full form of VRF.
Correct : A. voltage ripple factor
26. -Φ fully controlled rectifier is
Correct : B. 7th
27. to protect them from dust and contamination.
Correct : A. enclosures
28. voltage of a dc machine is a function of its magneto-motive force.
Correct : A. non-linear
29. compound dc motor is shown below. What conclusions can be made?
Correct : D. all of the mentioned
30. It is impossible to start a differential compounded dc motor.
Correct : A. true
31. compound motor and he has been asked to make it start. How will he try?
Correct : D. all of the mentioned
32. with compensating winding has a field current of 5 A to produce a voltage of 250 V at 1200 rpm. What will be the shunt field current of this machine at no load?
Correct : A. 5 a
33. b) position, then the
Correct : D. all of the mentioned
34. many types?
Correct : B. two
35. Rolling mills exhibit what type of load torque characteristics?
Correct : D. non-linearly decreasing torque characteristics
36. Torque inversely varies with the speed in the windage load torque component.
Correct : B. false
37. What type of force handles for active torques?
Correct : C. gravitational forces
38. Passive torques always oppose the motion of the driven machine.
Correct : A. true
39. Among the following which one exhibits linearly rising load torque characteristics?
Correct : D. separately excited dc generator connected to the resistive load
40. What is the condition for the steady-state operation of the motor?
Correct : C. load torque = motor torque
41. Choose the correct one. (* stands for multiplication, J represents the moment of inertia, w represents angular speed).
Correct : C. j*d(w)/dt = motor torque – load torque
42. Which of the following is the best braking method?
Correct : D. electric braking
43. DC motor is still widely used in tractions due to its excellent braking properties.
Correct : B. false
44. Which of the following is not the method of electrical braking?
Correct : D. eddy current
45. Which of the following is correct formula for braking torque in plugging?
Correct : A. n (ka2/rb)
46. Electrical braking of any variety becomes less effective as
Correct : B. speed decreases
47. Plugging is applied in a motor, if we don’t make the switch OFF what will happen?
Correct : B. motor will come to rest and will start rotating in another direction
48. Plugging is used in
Correct : A. small motors only
49. Which of the following is dynamic braking?
Correct : D. removal of armature circuit from current machine circuit
50. Braking time in the dynamic braking is the function of
Correct : D. all- system inertia, load torque and motor rating
51. In dynamic braking, when braking is applied system acts as
Correct : C. generator
52. In which of the following electrical braking method, energy is supplied back to the supply?
Correct : C. regenerative braking
53. connected across AC supply?
Correct : D. burn due to heat produced in the field winding
54. What will happen if the back emf of a DC motor vanishes suddenly?
Correct : C. the armature may burn
55. is DC motor and not an AC type?
Correct : C. commutator
56. can sustain the maximum temperature rise?
Correct : A. field winding
57. Direction of rotation of motor is determined by
Correct : D. fleming’s left-hand rule
58. of a motor?
Correct : D. output power available at the shaft
59. An electric motor is having constant output power. So, motor will have a torque speed characteristic
Correct : D. rectangular hyperbola
60. In which of the following case we will get maximum power?
Correct : C. supply voltage = 2 x ea
61. Sometimes motor has to be de-rated.
Correct : A. true
62. able to withstand
Correct : D. bending moment, unbalanced magnetic pull and twisting stains
63. present. The order of residual magnetism is
Correct : A. 2 to 3 per cent
64. Sparking is discouraged in a DC motor.
Correct : B. false
65. construction of single phase induction motor?
Correct : C. 5
66. What is the lamination used for the stator?
Correct : C. cast iron or die cast aluminium alloy frame
67. What type of coils are used for winding the single phase induction motor generally?
Correct : D. circular coils
68. How many kinds of single phase windings are present?
Correct : B. 3
69. How are the poles and pitches in the concentric windings?
Correct : A. single pole, different pitches
70. What is the form of the progressive windings?
Correct : B. single layer diamond coil windings
71. When is the skein winding made use of?
Correct : A. when small amount of relatively small size wire is used
72. winding made use of?
Correct : B. fractional horse power single phase induction motor
73. Which winding is mostly used winding in the single phase induction motor?
Correct : B. concentric winding
74. What is/are the advantages of the skein winding?
Correct : D. low cost to wind, low cost to insert, permits some freedom of choice of distribution
75. What material is used in the tunnel of the rotor of the single phase induction motor?
Correct : A. aluminium
76. What type of operations are used in the starting switches?
Correct : C. centrifugal operation and mechanical operation
77. The ac electrolytic capacitor is formed by winding two sheets of etched aluminium foil.
Correct : A. true
78. The electrolytic capacitor and insulator unit is impregnated using ethylene glycol or a derivative.
Correct : A. true
79. What is the range of the power factor of electrolytic capacitors?
Correct : C. 6-8
80. Why starters are required in a DC motor?
Correct : D. to restrict armature current as there is no back emf at starting
81. For which motors DOL starter can be used?
Correct : A. up to 5 h.p
82. A three-point starter is used for
Correct : B. shunt as well as compound motors
83. The starting resistance of a DC shunt motor is generally
Correct : A. low
84. without starter?
Correct : A. heavy sparking at brushes
85. Motor will start quickly when used without starter.
Correct : A. true
86. In shunt and compound motor starting the shunt field should be made on with full starting resistance in
Correct : C. series with armature
87. 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
88. γ is given as 1.585. Resistance at maximum allowable current is given equal to 4 Ω, what is the 5th step resistance?
Correct : A. 0.235
89. Four-point starter is used when
Correct : C. motor field current is varied over wide range
90. 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
91. A 100 hp, 250 V, 350 A shunt dc motor with an armature resistance of 0.05 ohms. To limit maximum starting current to twice the rated of its value, what will be the number of stages of starting resistances?
Correct : A. 3
92. b)
Correct : A. starting resistance would burn
93. (iv) Burning of the field winding
Correct : A. (i), (ii), (iii), (iv)
94. is/are
Correct : A. 3-point and 4-point starter
95. The direct-on-line starter is used to start a small dc motor because it limits initial current drawn by armature circuit.
Correct : B. false
96. over DOL starter due to
Correct : A. lesser losses
97. 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
98. The effect of fringing increases as we
Correct : A. increase air gap
99. is
Correct : D. none of the mentioned
100. If the students give a forward shift of 10° to the dc generator, then it