1.No-load speed of which of the following motor will be highest ?
2. The direction of rotation of a D.C. series motor can be changed by
3. Which of the following application requires high starting torque ?
4. If a D.C. motor is to be selected for conveyors, which motor would be preferred ?
5.Which D.C. motor will be preferred for machine tools ?
6. Differentially compound D.C. motors can find applications requiring
7. Which D.C. motor is preferred for elevators ?
8. If the field of a D.C. shunt motor gets opened while motor is running
9. Starters are used with D.C. motors because
10. In D.C. shunt motors as load is reduced
11.The type of D.C. motor used for shears and punches is
12. If a D.C. motor is connected across the A.C. supply it will
13. To get the speed of D.C, motor below the normal without wastage of electrical energy is used.
14. When two D.C. series motors are connected in parallel, the resultant speed is
15.The speed of a D.C. shunt motor more than its full-load speed can be obtained by
16. In a D.C. shunt motor, speed is
17. A direct on line starter is used: for starting motors
18. What will happen if the back e.m.f. of a D.C. motor vanishes suddenly?
19. In case of D.C. shunt motors the speed is dependent on back e.m.f. only because
20. In a D.C. shunt motor, under the conditions of maximum power, the current in the armature will be
21. By looking at which part of the motor, it can be easily confirmed that a particular motor is D.C. motor?
22. In which of the following applications D.C. series motor is invariably tried?
23. In D.C. machines fractional pitch winding is used
24. A three point starter is considered suitable for
25. In case-the conditions for maximum power for a D.C. motor are established, the efficiency of the motor will be
26. The ratio of starting torque to full-load torque is least in case of
27. In D.C. motor which of the following can sustain the maximum temperature rise?
28. Which of the following load normally needs starting torque more than the rated torque?
29. The starting resistance of a D.C. motor is generally
30. The speed of a D.C. series motor is
31. In a D.C. series motor, if the armature current is reduced by 50%, the torque of the motor will be equal to
32. The power mentioned on the name plate of an electric motor indicates
33. Which D.C. motor has got maximum self loading property?
34. Which D.C. motor will be suitable along with flywheel for intermittent light and heavy loads?
35. If a D.C. shunt motor is working at no load and if shunt field circuit suddenly opens
36. For the same H.P. rating and full load speed, following motor has poor starting torque
37. D.C. series motors are used
38. In case of conductively compensated D.C. series motors, the compensating winding is provided
39. Which of the following motor is preferred for operation in highly explosive atmosphere ?
40. If the supply voltage for a D.C. motor is increased, which of the following will decrease ?
41.Sparking at the commutator of a D.C. motor may result in
42. Which one of the following is not the function of pole shoes in a D.C. machine ?
43. The mechanical power developed by a shunt motor will be maximum when the ratio of back e.m.f. to applied voltage is
44. For which of the following applications a D.C. motor is preferred over an A.C. motor ?
45. In D.C. machines the residual magnetism is of the order of
46. Which D.C. motor is generally preferred for cranes and hoists ?
47. Three point starter can be used for
48. Sparking, is discouraged in a D.C. motor because
49. Speed control by Ward Leonard method gives uniform speed variation
50. Flywheel is used with D.C. compound motor to reduce the peak demand by the motor, compound motor will have
51. Following motor is used where high starting torque and wide speed range control is required.
52. In a differentially compounded D.C. motor, if shunt field suddenly opens
53. Which of the following motor has the poorest speed regulation ?
54. Buses, trains, trolleys, hoists, cranes require high starting torque and therefore make use of
55.As the load is increased the speed of D.C. shunt motor will
56. The armature torque of the D.C. shunt motor is proportional to
57. Which of the following method of speed control of D.C. machine will offer minimum efficiency ?
58. Usually wide and sensitive speed control is desired in case of
59. The speed of a motor falls from 1100 r.p.m. at no-load to 1050 r.p.m. at rated load. The speed regulation of the motor is
60.The armature voltage control of D.C. motor provides
61. As there is no back e.m.f. at the instant of starting a D.C. motor, in order to prevent a heavy current from flowing though the armature circuit
62. The speed of a D.C. shunt motor can be increased by
63. In case the back e.m.f. and the speed of a D.C. motor are doubled, the torque developed by the motor will
64. At the instant of starting when a D.C. motor is put on supply, it behaves like
65.Which one of the following is not necessarily the advantage of D.C. motors over A.C. motors ?
66. The plugging gives the
67. If the terminals of armature of D.C. motor are interchanged, this action will offer following kind of braking
68. Which of the following motors one will choose to drive the rotary compressor ?
69.Why are the D.C. motors preferred for traction applications ?
70.Which of the following motors is most suitable for signalling devices and many kinds of timers ?
71.Ward-Leonard control is basically a
72. In Ward-Leonard control the lower limit of speed is imposed by
73. The main disadvantage of the Ward-Leonard control method is
74. Regenerative method of braking is based on that
75. The hysteresis loss in a D.C. machine least depends on
76. The losses occurring in a D.C. generator are given below. Which loss is likely to have highest proportion at rated load of the generator ?
77. In a manual shunt motor starter
78. Which of the following loss/losses in a DC generator is dissipated in the form of heat?
79. The total losses in a well-designed DC generator of 10 kW will be nearly equal to ________
80. DC generators are normally designed for maximum efficiency at or near ____________
81. The condition for maximum efficiency for a D.C. generator is
82. In a DC generator, the iron losses mainly take place in ____________
83. The purpose of retardation test on D.C. shunt machines is to find out
84. Which of the following tests will be suitable for testing two similar D.C. series motors of large capacity ?
85.Hopkinson’s test on D.C. machines is conducted at
86. During rheostat braking of D.C. series motors
87. Which method of braking is generally used in elevators ?
88. In variable speed motor
89. Where D.C. motor of H.P. 12 or more requires frequent starting, stopping, reversing and speed control
90.If a D.C. shunt motor is working at full load and if shunt field circuit suddenly opens
91. D.C. motor is to drive a load which has certain minimum value for most of the time and some peak value for short duration. We will select the
92. D.C. motor is to a drive a load which is almost nil for certain part of the load cycle and peak value for short duration. We will select this
93. Which D.C. motor has got maximum self relieving property ?
94. Which of the following could be lamina-proximately the thickness of laminations of a D.C. machine ?
95. The field coils of D.C. generator are usually made of
96. The commutator segments are connected to the armature conductors by means of
97. In a commutator
98. In D.C. generators the pole shoes are fastened to the pole core by
99. The bearings used to support the rotor shafts are generally
100. Copper brushes in D.C. machine are used
101.In D.C. generators, the cause of rapid brush wear may be
102. In case of D.C. machines, mechanical losses are primary function of
103. Iron losses in a D.C. machine are independent of variations in
104. In D.C. generators, current to the external circuit from armature is given through
105.In case of a 4-pole D.C. generator provided with a two layer lap winding with sixteen coils, the pole pitch will be
106. The insulating material used between the commutator segments is normally
107. In D.C. generators, the brushes on commutator remain in contact with conductors which
108. If brushes of a D.C. generator are moved in order to bring these brushes in magnetic neutral axis, there will be
109. Armature reaction of an unsaturated D.C. machine is
110. Eddy currents are induced in the pole shoes of a D.C. machine due to
111.D.C. generators are connected to the busbars or disconnected from them only under the floating condition
112. Equilizer rings are required in case armature is
113. Welding generator will have
114. In case of D.C. machine winding, number of commutator segments is equal to
115.In a D.C. machine, short-circuited field coil will result in
116. For a D.C. machines laboratory following type of D.C. supply will be suitable
Explain:- Rotary Converter:
A rotary converter is a type of electrical machine which acts as a mechanical rectifier, inverter, or frequency converter. It is used to convert AC to DC or DC to AC power, before the advent of chemical or solid-state power rectification and inverting. They are commonly used to provide DC power for laboratories and also can use for commercial purposes.
Mercury arc rectifier:
A mercury arc rectifier is a type of electrical rectifier used for converting high-voltage or high-current alternating current (AC) into direct current (DC). This power of converting is basically through a large-scale. The operation of the rectifier relies on an electrical arc discharge between electrodes in a sealed envelope containing mercury vapor at very low pressure.
Motor-Generator set:
They consist of a (3-phase) motor either Synchronous motor or Induction motor, directly coupled to a DC generator As the motor speed depends mainly on the mains frequency, these units are relatively insensitive to variations in the supply voltage The cost of a motor-generator set is high and widely used in welding sets.