1.3 point starters are not suitable for applications where speed variation by flux control is required because the motor may
Stop at very high speed
2. A 200V dc machine has Ra=0.5.I f the full load armature current is 30A, the induced emf when the machine runs
1. as a generator
2. As a motor will be respectively :-> 215V, 185V
3. A 220V dc machine has Ra=1o ohm If the full load current is 20 A. The difference in the induced voltages when the machine is running as a motor and as a generator
:-> 40V
4. A 3-phase squirrel cage induction motor has a full -load efficiency of 0.8 and a maximum efficiency of 0.9. It is operated at a slip of 0.6 by applying a reduced voltage. The efficiency of the motor at this operating point is
:-> Less than 0.4
5. A 3point starter is considered suitable for DC _ _ _ _ _ _ _ motors
:-> Shunt
6. A cumulatively compound generator is supplying 20A at 200V.Now if the series field winding is short circuited the terminal voltage will
:-> become less than 200V
7. A dc generator beyond critical resistance will generate
:-> No voltage
8. A dc generator is employed
:-> As a booster to maintain the constant voltage at load end of the feeder
9. A dc motor can be easily identified by looking at
:-> Commentator
10. A DC motor is operating at no-load. If the armature is shunted by a resistance its speed will
:-> decrease
11. A dc series generator is provided with diverter and is delivering its rated current. if the diverter switch is opened , the terminal voltage will
:-> increase
12. A dc series motor develops a torque of 20N-M at 3A of load current .If the current is increased to 6A the torque developed will be
13. A dc series motor must not be started on no-load because it would
:-> run at dangerous speed
14. A DC shunt motor is driving a mechanical load at rated voltage at normal excitation. If the load torque is increased to double of the normal one, the speed of the motor will
:-> Fall slightly
15. A DC shunt motor is running at light load, what will happen if the field winding gets opened?
:-> Motor will pick up high speed
16. A double cage induction n motor is a
:-> squirrel cage type
17. A large DC shunt motor can be started preferably using a
:-> Compensator
18. A separately exited dc generator has an open circuit voltage Eon for a certain value of field current .If the field current is halved, the open circuit voltage will be . c 2Eo
:-> may be Eo/2 or More than Eo/2
19. A series generator can excite itself
:-> only when lo ad current is not zero
20. A series motor is working drawing a load current of 1A from the lines. If now the load is reduced such that the current drawn is halved, the speed of the machine (neglecting the saturation and are mature resistance) would be
:-> increased by 100 %
21. A squirrel cage induction motor is not favored when _ _ _ _ _ is the main consideration
:-> High starting torque.
22. A thicker wire is used in a dc series motor field winding than that in a dc shunt motor
:-> To create more flux
23. An electric train employing a dc series motor is running at affixed speed when a sudden slight drop in the mains voltage occurs this would result in
:-> drop in speed and rise in current
24. An exciter for turbo generator in a dc--------- ---generator
:-> Shunt
25. An external resistance added in the field circuit of a dc shunt generator will cause
:-> Decrease in terminal voltage
26. An induction motor can run at synchronous speed if it is operated.
:-> With emf injected in the rotor circuit
27. An induction motor employs a starting device to restrict _ _ _ _ _ at start.
:-> line current
28. DC compound motors are generally
:-> Cumulative compound
29. DC generators are connected to or disconnected from the bus- bar only under the floating condition. This is done to avoid
:-> Burning of switch, sudden loading of the prime mover, mechanical jerk to the shaft
30. DC machines are generally designed for maximum efficiency around
:-> Full load
31. Dc shunt motor runs at rated speed, if its field circuit gets opened then soon after this the motor speed will tend to
:-> Increase
32. Direct-online starters are not suitable for starting large DC motors, because
:-> The starting current will be enormously high, which will cause large voltage drop in the supply mains
33. Efficiency of a dc machine is maximum when the variable losses are equal to
:-> Constant losses
34. Efficiency of a dc shunt machine can be computed by knowing
:-> Output, input, rating, armature resistance of the machine
35. Equalizer bar is necessary for parallel operate on of dc _ _ _ _ _ _ _ _ generators
:-> Series and over compound
36. Field copper losses are constant in DC _ _ _ _ _ _ _ motors
:-> Shunt
37. For a specific o pen circuit voltage of a dc generator the short circuit current will be maximum value when n it is: ->cumulatively compound
38. For parallel operation dc generator general y prefer ed are
:-> Both shunt and under compound
39. For small values of armature current Ia, the tor queue developed by a dc series motor is proportional to
:-> Ia2
40. For the same power output rating and full load speed, the motor that will have poorest starting torque, is
:-> Differential compound
41. For very sensitive and wide speed control, the preferable control method is
:-> ward-Leonard system
42. If a current carrying coil is placed in a uniform m magnetic field with its place perpendicular to the direction of magnetic induction then
:-> The net force and torque both on the coil are zero
43. If field of one of 2 generators operating in parallel made very week, then it will
:-> operate as a motor and run in the same direction
44. If N is the speed of the dc series motor and Ia is the armature current then
:->Na 1/Ia
45. If one generator is to be taken out of 2 generators operating in parallel
:-> The excitation of first is reduced and of the second is increased gradually and simultaneously
46. If the back elf in a dc motor vanishes suddenly, the motor will
:-> burn
47. If the field applied across the armature of a DC motor is reduced by 5 % keeping the load current and field current unchanged. The speed of the motor will
:-> reduce by about 5 %
48. If the field circuit resistance of a dc shunt generator exceeds its critical value, the generator
:-> Fails to build up
49. If the flux of a DC motor approaches zero, its speed will
:-> Approach infinity
50. If the handle of a 3point starter goes back to OFF position, it may be due to
:-> Over load
51. If the no voltage release in DC motor starter fails to operate on failure supply, on resumption of supply the motor will
:-> Get damaged due to flow of excessive current in armature
52. In a 3-phase induction motor the relative speed o f stator flux is zero with respect to
:-> Rotor flux
53. In a 3- phase induction motor, the regeneration braking occur when
:-> The load is lowered by a hoisting machine
54. In a DC compound motor the field regulator is provided to
:-> Control the flux
55. In a DC compound motor, the series field in comparison to shunt field will have
:-> Less turns of thick wire
56. In a dc generator the critical resistance refers s to the resistance of
:-> field
57. In a dc machine mechanical losses are primarily function of
:-> Speed
58. In a dc machine mechanical losses occur due to
:-> Brush friction, bearning friction, air resistance
59. In a dc machine the angle between main field axis and brush axis is kept 90 inorder to have
:- >maximum torque
60. In a dc machine the constant losses are
:-> Shunt field copper loss, Iron or mechanical loss
61. In a dc motor the wind age loss is proportional to
:-> Square of armature speed
62. In a dc series motor if armature current is reduced to 70 % of its original value the torque of the motor will be reduced by
:-> 51 %
63. In a dc series motor the torque developed is
:-> Proportional to the square of the armature current
64. In a dc shunt generator, the voltage build up is generally restricted due to
:-> Saturation of iron
65. In a DC shunt motor, the 3po into starter
:-> Limits starting currant, provides protection ageist overload & No-volt
66. In a de motor which of the following can sustain the maximum temperature rise?
:-> field windings
67. In a rotating electric machine when the two magnetic fields are aligned with each other the torque produced will be:
->Zero
68. In a ward-Leonard drive, if the field current o f DC generator is suddenly reduced the controlled DC motor operates
:-> In dynamic braking mode
69. In arc welding in order to obtain steady arc on should use
:-> Differentially compound
70. In armature control method of speed control of DC motors
:-> Armature circuit resistance is changed
71. In case of a conductively compensated dc series motor, the compensating winding is provided:
->in series with armature winding
72. In case of a dc series motor it is possible to have finite no load speed if a resistance is connected across its
:-> Armature terminal less
73. In case of dc shunt motors, the regenerative braking is employed when the load
:-> Has overhauling characteristics
74. In dc generator the residual magnetism is of the order of
:-> 2.5 %
75. in dc machines
:-> Induced elf and torque are produced in both motor and generator
76. in direct method of determination of efficiency of a dc machine
:-> The machine is actually loaded and input power and output power are measured
77. In Hopkinson’s and field's test the main common n thing is that
:-> Both test use two identical mechanically coupled dc machines
78. In Hopkinson’s efficiency test for dc machines
:-> One machine acts as generator and another as motor
79. In parallel operation of 2 dc compound generators provided with inter poles, the equalizing bar connected to
:- >junction of series and interpole fields
80. In regenerative braking, the motor energy is
:-> Returned to the supply mains
81. In rotating electric machine the torque produced will be maximum. When
:-> Torque angle is 90
82. In Swinburne’s test of a dc machine
:-> No-load losses are measured and copper losses are calculated
83. In Swinburne’s test of determination of the efficiency of a dc shunt machine the no-load input power supplies
:->Armature , iron, f iction, windage, losses
84. In the case parallel operation dc compound wound generators, for proper division of load from no l oaf to full load it is essential that they should have the same
:-> Percentage regulation
85. In ward- Leonard drive, if the field current o f the DC generator is suddenly reduced, the controlled DC motor operates
:-> In regenerative braking mode
86. In ward- Leonard method of speed control, the direction of rotation of motor is reversed usually b y reversing the connections of the
:-> Generator field terminals
87. In ward-loenard system, the lower limit of speed is imposed by
:-> Residual magnetism of the generator
88. Ina de motor speed control by varying the armature circuit resistance provides?
:-> Constant torque drive
89. Lubricant used for ball bearings is usually
:-> Grease.
90. Modern alternators are designed to have poor regulation as it
:-> limits the value of short-circuit current
91. Modern alternators are designed to have poor regulation as it
:-> limits the value of short-circuit current
92. Over or under compounding of dc generator is achieved by
:-> hunting more or less current from the series field
93. Regenerative braking is based on that the back EMF is
:-> More than applied voltage
94. Rhemagnitude of mechanical force in a dc motor is depend ento n
:-> Length of the conductor
95. Shunt compound (long shunt an ideal Dc generator has a regulation of -----percentage :-> Zero
96. Squirrel cage induction motors have the disadvantages of
:-> High sensitivity to fluctuations in supply voltage and low power factor at light -load.
97. T is the load torque o f a dc series mo tor having linear magnetization and negligible armature resistance then the speed of the motor is
:-> Inversely proportional to
98. The air gap between the stator and armature of an electric motor is kept as small as possible in order to
:- >give stranger magnetic field
99. The armature MMF wave in a DC machine is
:-> Triangular
No comments:
Post a Comment