3 q induction motor

OBJECTIVE ELECTRICAL ENGINEERING 3 Q INDUCTION MOTORS

1. The frame of an induction motor is usually made of

(a) Cast iron(b) Silicon steel(c) Aluminium(d) Browge

Ans a

2. Which of the following component of induction motors is usually fabricated of the silicon steel

(a) Shaft(b) Bearings(c) Stator core(d) None of the above

Ans a

3. Which type of bearing is use to support to rotor shaft of an induction motor

(a) Bush-bearing(b) plummer(c) Ball bearing(d) Magnetic bearing

Ans c

4. The shaft of an induction motor must be

(a) Flarible(b) Stiff(c) Hollow(d) Any of above

Ans c

5. The shaft of induction motor is made of

(a) Carbon steel(b) High speed steel(c) Stain less steel(d) Cast iron

Ans a

6. In the stator core of an induction motor the winding is

(a) Flushed with core(b) Housed in slots(c) Welded to frame(d) Supported on bolts

Ans b

7. In an induction motor on no load the slip is generally

(a) 4%(b) 1.5%(c) 2%(d) Less than 1%

Ans d

8. A 400 KW 3 Q, 440 volt, Hz 50, induction motor has a speed of 950 rpm on full load. The machine has 6 pole. The slip of machine will be

(a) 0.6 (b) .04(c) 0.10(d) .05

N = 120f/p = 120X50/6=1000 rpm

S = 1000-950/1000 = Ns-N/Ns = 50/1000 =1/20 = 0.5

Ans d

9. In which condition the operating speed of an induction motor will be closer to synchronous speed

(a) Fluctuating load(b) Over load(c) Normal load(d) No load

Ans d

10. The ratio of resistance to reactance for an induction motor under starting condition should be

(a) High (b) Unity(c) Less than unity(d) Negligible

Ans d

11. In medium size induction motor, the slip is generally around

(a) .04%(b) 0.4%(c) .4%(d) 14%

Ans c


12. In square cage induction motor, the rotor slot are generally give slight skuw in order to

(a) Reduce magnetic humm(b) Reduce windage losses(c) Reduce eddy current loss(d) Reduce accumulation of dust and

dirt

Ans a

13. In the case of air gap in an induction motor is increases

(a) The windage loss will increase(b) Power fector will decrease(c) Speed of motor will increase(d) The magnetic current of the rotor

will decrease

Ans b

14. Slip rings are generally made of

(a) Aluminium(b) Copper(c) Carbon(d) Phos phors bronze

Ans d

15. Which of the following is preffered rpm for 4 pole induction motor

(a) 1425 rpm(b) 1460 rpm(c) 1440 rpm(d) 1420 rpm

Ans c

16. The copper loss in the rotor of induction motor

(a) Result in eddy current(b) Are loss as heat(c) Result in noise(d) Are always negligible

Ans b

17. Which of the following application generally needs high speed motor

(a) Lath machine(b) Reciprocating air compressure(c) Flour mills(d) Air blower

Ans d

18. The (n) efficiency of an induction motor can be expected to be nearly

(a) 99%(b) 80-90%(c) 95-98%(d) 60-80%

Ans c

19. Which of the following induction motor will need largest diameter shaft

(a) 20 HP-2880 RPM(b) 20 HP-1440 RPM(c) 20 HP-960 RPM(d) 20 HP -720 RPM

Ans d

20. The no. of slip rings on square cage induction motor is usually

(a) 4(b) 2(c) -3(d) No slip ring

Ans d

21. The starting torque of a squarl cage induction motor is

(a) Negligible(b) Low(c) Same as full load torque (d) Lightly more than full load torque

Ans b

22. The slip of an induction motor will be low when

(a) Rotor resistance is high(b) Rotor resistance is low(c) Winding loss is least(d) Bearing friction is low

Ans b

23. In a cage induction motor if the material of greater resistivity than copper is used for end rings. This is likely to result in

(a) Reduction in efficiency(b) Increase in slip(c) Increase in rotor temperature

rise


(d) All of the above

Ans d

24. Double squarl cage induction motor has

(a) Two parallel windings in the stator

(b) Two parallel windings in the rotor(c) Tow series windings in the stator(d) None of the above

Ans b

25. The ratio of starting torque to normal torque will be highest when starting the motor by

(a) Star-delta starter(b) Direct on line starter(c) Auto T/F starter with 50% tepping(d) None of the above

Ans b

26. The ratio starting torque to normal torque will be least when starting the motor by

(a) Star-delta starter(b) D.O.L starter(c) Auto T/F starter with 50%

copping(d) None of the above

Ans a

27. Which of the following method of starting an induction motor does not result in reduced voltage supply to the motor while starting

(a) Star-delta starter(b) Auto T/F starter(c) D.O.L starter(d) All of the above

Ans c

28. During the star-delta starting the motor is initially run

(a) Direct on line(b) In star(c) In delta(d) Any of the above

Ans b

29. During star-delta staring of induction motor, during star

connections, the voltage apply to end phase in

(a) 1/3 of the normal voltage(b) 1 3 of the normal voltage(c) 3 of the normal voltage (d) None of the above

Ans b

30. Star delta starting is not possible ( of induction motor) in case of

(a) High speed motor(b) Low horse power motor(c) Variable speed motor(d) Single phase motor

Ans d

31. The turn clogging is associated with

(a) Induction motor(b) D.C series motor(c) Compound generator(d) 3 Q transformer

Ans a

32. In which of the following motor, speed can be controlled through rotor side

(a) A.c series motor(b) D.c series motor(c) 3 Q slip ring induction motor(d) 3 Q squarl cage induction motor

Ans c

33. In case of induction motor the torque is

(a) Directly proportional to slip(b) Inverselly proportional to slip(c) Directly proportional to slip2

(d) Inversely proportional to /slip2

Ans a

34. The speed of induction motor its slip is 100% will be

(a) Synchronous speed(b) Rated speed(c) Full load speed(d) Zero speed

Ans d


35. The speed of air induction motor will be same as synchronous speed when slip is

(a) Infinity(b) Unity(c) Zero(d) 0.5

Ans c

36. Step less speed controlled of induction motor is possible by which of the following method

(a) Changing the no. of pole(b) E.m.f injucted in rotor circuit(c) Casecade operation(d) None of the above

Ans b

37. For average induction motor the pull out torque

(a) Same as normal full load torque(b) One and half time of full load

torque(c) Two and a half time of full load

torque(d) None of the above

Ans b

38. For average induction motor the pull out torque is

(a) Same as normal full load torque(b) One and a half time of full load

torque (c) Two and a half time of full load

torque(d) None of the above

Ans c

39. During which following test on induction motor reduced voltage is applied

(a) Load test(b) No load test(c) Stator resistance test(d) Blocked rotor test

Ans d

40. Rotor rheostate control method for speed control is used for

(a) Slip ring induction motor only(b) Squarl cage induction motor only(c) Both a and b

(d) None of the above

Ans a

41. In the circle diagram of for induction motor, the diameter of circle represent

(a) Line voltage(b) Running torque(c) Rotor current(d) Slip

Ans c

42. For which motor the speed can be controlled from rotor side

(a) Slip ring induction motor(b) Squarl cage induction motor(c) Both a and b(d) None of the above

Ans a

43. If any two for the induction motor are the interchanged

(a) Motor will be burn(b) The motor will not run(c) The motor will run at reduced

speed(d) The motor will run in reverse

direction

Ans d

44. The rotor of 3 Q induction motor rotor in same direction as that of the revolving field, which of the following low is associate with above phenomenon

(a) Lenz’s low(b) Feraday’s low(c) S(d) Flamings low

Ans a

45. An induction motor is(a) Non self starting(b) Self starting with low torque (c) Self starting with high torque(d) Self starting with zero torque

Ans b

46. The maximum torque in an induction motor is depends on

(a) Frequency


(b) Rotor inductive reactance(c) Square of the supply voltage(d) All of the above

Ans d

47. In 3 Q induction motor the frequency of the induced e.m.f of in rotor circuit is

(a) Maximum at synchronous speed(b) Maximum at stand still(c) Minimum at stand still(d) Zero at stand still

Ans b

48. In an induction motor the synchronous speed of revolving field depends on all of the following except

(a) No.of poles(b) Supply frequency(c) Flur density(d) None of the above

Ans c

49. In 3 Q squarl cage induction motor

(a) Rotor conductor ends are short circuited through slip rings

(b) Rotor conductor ends are short circuited through end rings

(c) Rotor conductor are kept open(d) Rotor conductors are connected

to insulation

Ans b

50. In a 3 Q motor no. of poles in the rotor winding are always

(a) Zero(b) More than the no. poles in stator

winding(c) Less than the no. of poles in

stator winding(d) Equal to the no. of poles in stator

winding

Ans d

51. D.O.L starting of induction motor is usually restricted to

(a) High speed motor(b) High horse power motor(c) Variable speed motor(d) Low horse power motor

Ans b

52. Rotor terminals of 3 Q slip ring induction motor are open circuited in case supply in case supply voltage given to stator, then

(a) Motor will burn(b) Motor will not run(c) The motor will run at reduced

rpm(d) The motor will run at increased

rpm

Ans b

53. 10 HP, 3 Q induction motor will following rpm are available, which motor will have highest cost as compare to the remaining


Ans d

54. No load current in 3 Q induction motor is nearly

(a) 0.1% of full load current(b) 1-5% of full load current(c) 15-25% of full load current(d) 50-60% of full load current

Ans c

55. It is advice line starting of induction motor and using starter be cause

(a) Starting torque is very high(b) Motor takes five to seven time its

full load current(c) It will pick up very high speed

and many go out to step(d) It will run reverse direction

Ans b

56. When using star-delta starter which of the following is reduced during starting

(a) Current(b) Power fector (c) Voltmeter(d) KW of motor

Ans a


57. The speed of squarl cage induction motor can be controlled by all of the following method except

(a) Reducing supply voltage(b) Changing no. of poles(c) Changing supply frequency(d) Changing rotor winding

resistance

Ans d

58. When the input voltage and frequency of 3 Q induction motor is halfed, the following phenomenon is observed apparoximatly

(a) The air gap flux is halfed(b) The maximum torque is ahlfed(c) The maximum torque remain

same(d) None of the above

Ans b

59. The crawling in an induction motor is called by

(a) Low voltage supply(b) High load(c) Improved design of machine(d) Harmonic develop in the motor

Ans d

60. The P.F of induction motor under no load condition will be closed to

(a) 0.2 leading(b) 0.2 lagging(c) 0.5 leading(d) Unity

Ans b

61. A 3 Q, 400 volt, 60 Hz , 960 rpm induction motor is run on 50 Hz supply the motor will

(a) Burrent out(b) Not run(c) Run at more than 960 rpm(d) Run at less than 960 rpm

Ans d

62. The clogging of induction motor can be avoided by

(a) Using D.O.L starter(b) Auto T/F starter

(c) Proper ventilation(d) Having no. of rotor slots prime to

the no. of stator slots

Ans d

63. One phase of 3 Q partly loaded induction motor supply got opened up while the motor was in motion, this is likely to result in

(a) Stallings of the motor(b) Burning of one phase winding of

the motor (c) Burning of all 3 Q of winding of

the motor(d) Understand running of motor

Ans d

64. If an induction motor with certain ratio of rotor to stator slots run at 1/7 of the normal speed. The phenomenon will turned as:

(a) Hunting (b) Crawling(c) Cogging(d) Humming

Ans b

65. In case the line voltage of an induction motor is reduced by 10% of its rated value, the starting current will be

(a) Reduced by 10%(b) Reduced by 5%(c) Increased by 5%(d) Increased by 10%

Ans a

66. Single phasing preventers are used in

(a) Step up transformer(b) Step down transformer(c) Induction motors(d) All of the above

Ans c

67. Various method for starting of an induction motor are listed below which method requires starter terminals

(a) Rotor rheostate(b) Auto T/F starter (c) D.O.L starter


(d) Star-delta starter

Ans d

68. For a 3 Q cage induction motor having delta connected rotor the no. of slip rings will be

(a) Zero(b) 1(c) 2(d) 3

Ans a

69. The speed load characteristic of an induction motor closely resembles the speed load characteristic which of the following motor

(a) D.C series motor(b) D.C shunt motor(c) Universal motor(d) None of the above

Ans b

70. In a slip ring induction motor resistance is connected in rotor this is

(a) To limit the starting current(b) Increase to starting torque(c) To increase the starting current(d) None of the above

Ans b

71. Which type of hearing is provided in small induction motor to support the rotor shaft

(a) Bush bearing(b) Cast iron bearing(c) Ball bearing(d) None of the above

Ans c

72. In case of 100 kw induction motor, the slip is expected to the around

(a) 10%(b) 4%(c) 7%(d) 105 to 2%

Ans d

73. In an induction motor when the now of stator and rotor state is equal and motor refuse to start, the phenomenon is turned as:

(a) Crawling(b) Cogging(c) Short circuiting(d) Humming

Ans b

Variation in torque and speed of an electric motor due to

Variation in magnetic flew as rotor poles move passed stator poles

74. 5 HP, Hz 50, 3 Q 440 volt induction motor are variable for the following rpm, which motor will have highest(n) efficiency


Ans a

75. A pump injuction motor to switched on the supply 30% lower than its rated voltage the pump runs that will eventually happen it will

(a) Stal immideatly(b) Stal after same time(c) Continuous to run at lower speed

with out damage(d) Get heated and consequently get

damage

Ans d

76. 5 HP, 50 Hz, 3 Q 440 volt induction motors are available following no. of poles, which motor will have highest value of P.F

(a) 2 pole(b) 4 pole(c) 8 pole(d) 16 pole

Ans a


77. A 3 Q slip ring induction motor has

(a) Short circuited rotor(b) Wound rotor(c) Double cage rotor (d) Any of the above

Ans b

78. The locking tendency in 3 Q induction motor is reduced by

(a) Running the motor in reverse direction

(b) Using auto T/F starter for starting(c) Skewing in slots(d) Making the rotor slots parallel to

shaft

Ans c

79. In squarl cage induction motor starting current usually

(a) Less than full load current(b) Equal to the full load current(c) Slightly more than full load

current(d) 5 to 7 time than full load current

Ans d

80. A 3 Q squarl cage induction motor is useful when the motor has to start

(a) On-no load(b) Against light load(c) Against full load(d) Against over load

Ans b

81. The torque produce in an induction motor is nearly proportional to

(a) 1 applied voltage(b) Applied voltage(c) Applied voltage2


Ans c

82. The main function of starter for 3 Q induction motor is

(a) To provide high starting voltage(b) To provide high starting current(c) To limit the starting current(d) To limit the starting voltage

Ans c

83. What will happened in case the starter is not used on an induction motor

(a) Motor winding will burn(b) Motor will have tendency to crawl(c) There will be the heavy voltage

drop alone the line(d) None of the above

Ans c

84. Reduce voltage starter can be used with

(a) Squarl cage induction motor only(b) Slip ring induction motor only(c) Both a and b(d) None of the above

Ans c

85. Which of the following is class’C’ insulation

(a) Taflon (b) Mica(c) Paper(d) Cloth

Ans b

86. Short circuit test on an induction motor can not be use to determined

(a) Copper losses(b) Transformation ratio(c) Power scale of circle diagram(d) Windage less

Ans d

87. In an induction motor(a) Iron losses in stator will be

negligible as compare to that of the rotor

(b) Iron losses in rotor will be negligible as compare to that of the stator

(c) Iron losses in stator will be loss than the rotor

(d) Iron losses in stator will be more than the rotor

Ans d

88. Single phase preventor is used in


(a) Single phase motor(b) Universal motor(c) 3 Q induction motor with stator is

star connected(d) 3 Q induction motor with stator in

delta connected

Ans d

89. Synchronous watt age on an induction motor implies

(a) Stator input in watt(b) Rotor input in watt(c) Rotor out put in watt(d) Total input in watt

Ans b

90. A motor rated to run at 440 volt is running on normal voltage, suddenly voltage is dropped to 340 volt, the motor will be.

(a) Stop immediately(b) Heated up excessevly(c) Run in reverse direction (d) Draw reduced current

Ans b

91. For a 3 Q induction motor to develop maximum torque the phase difference between stator flux and the rotor current will be

(a) 00 electrical(b) 900 electrical(c) 450 electrical(d) 1200 electrical

Ans b

92. Which of the following can not the cause of over heating of a 3 Q induction motor

(a) Over loading(b) Stalling of rotor(c) To frequency starting and

stoping(d) High voltage supply

Ans d

93. A 3 Q induction motor when connected in star take 10 ampere when connected in delat it will take

(a) 5 A(b) Less than 10 ampere(c) 10 ampere

(d) More than 10 ampere

Ans d

94. A 440 volt, 50 Hz, 4 pole 3 Q induction motor has 4% slip the relative speed between rotor and stator magnetic field will be

(a) 1560 rpm(b) 1500 rpm(c) 1440 rpm(d) Zero rpm (none of the above)

Ans d

95. In case of 3 Q induction motor’ plugging’ means

(a) Putting the motor direct on line with out a starter

(b) Locking of rotor due to harmonic (c) Starting the motor on a load

which is more than rated load(d) Inter changing to supply phases

for quick stopping

Ans d

96. Which of the following is nest method for removing dust and particuls from an electric motor

(a) rubbing with cloth(b) Using wire brush(c) Passing compressed air(d) Vaccume suction

Ans d

97. When all the (3Q) three phases of an induction motor burn out, the probably cause be

(a) Single phasing(b) Unbalanced load(c) Unbalanced supply(d) Over load

Ans d

98. In case of 3 Q induction motor a fuse normally provided protection against

(a) High voltage(b) Over loaded(c) Short circuit (d) Single phasing

Ans c


99. Which of the following test data in required to draw a circle diagram of an induction motor

(a) Block rotor test only(b) No load test only(c) Stator test only(d) All of the above

Ans d

100. The slip of 5HP,3Q 440 volt, 50 Hz, 1440 rpm motor is s=1, it can be concluded that

(a) Motor is running at synchronous speed

(b) Rotor rpm is 1440(c) Rotor rpm is (100-1)X 1440 rpm(d) Rotor is not rotating

Ans d

101. The full load current for a 3Q, 440 volt, 20 HP induction motor will be closer to

(a) 5A(b) 15A(c) 25A(d) 35A

Ans c

102. The harmonic induced in induction motor can be induce by

(a) Using bush bearing(b) Squewing (c) Large air gap(d) Chording

Ans d

103. Which of the following is not a trade name of electric motor in india

(a) kirlosar(b) tata(c) jyoti(d) Crompton

Ans b

104. In 3Q induction motor same time copper bars placed drop in the rotor to

(a) Improve P.F(b) Improve efficiency(c) Reduce copper losses(d) Improve starting torque

Ans d

105. In a 3Q induction motor(a) Power fector at starting is the

same as that while running(b) Power fector at starting is low as

compare to that while running(c) Power fector at starting is high as

compare to that while running(d) None of the above

Ans b

106. The circle diagram of an, induction motor can not be use to determined

(a) Frequency(b) Out put(c) Power fector(d) Efficiency

Ans a

107. The current taken by a 3Q induction motor during plugging will be

(a) Normal full load current(b) More than blocked rotor current(c) Equal to blocked rotor current(d) Less than blocked rotor current

Ans b

108. Blocked rotor test in an induction motor is use to find out

(a) Short circuit current under rated voltage

(b) Leakage reactance(c) P.F an short circuit(d) All of these

Ans d

109. Lubricant for ball bearing is used

(a) Graphite(b) Grease(c) Mineral oil(d) None of the above

Ans c

110. Which of the following can be reduced by skewing in induction motor

(a) Noise(b) Vibration


(c) Synchronous motor(d) All of the above

Ans d

111. Which motor is preffer for used in mines, where explosive gases exists:

(a) Synchronous motor(b) D.C shunt motor(c) Induction motor(d) Air motor

Ans d

112. When a star-delta starter is used with 3Q induction motor

(a) A starting current reduced but starting torque increases

(b) Starting current increased but starting torque reduces

(c) Both starting current as well as starting torque reduces

(d) Both starting current as well as starting torque increases

Ans c

113. Ball-bearings are usually made of

(a) Cost iron(b) Stainless steel(c) High speed steel(d) Carbon crome steel

Ans d

114. The torque developed by a 3Q induction motor is least depends upon

(a) Shaft diameter(b) Rotor e.m.f (c) Rotor power fector(d) Rotor current

Ans a

115. Under which of the following circumstances a wound rotor induction motor will be preferred over squarl cage induction motor

(a) When the cost is major consideration

(b) When maintainence cost is to be kept low

(c) When wide range of speed control desired


Ans c

116. In an induction motor, if air gap is increased

(a) P.F will be low(b) Windage loss will be more(c) Bearing friction will be reduced(d) Copper loss will be reduced

Ans a

117. The frame of induction motor is generally made of

(a) Aluminium (b) Copper(c) Cost iron(d) Stainless steel

Ans c

118. The condition for maximum torque stands still in case of induction motor is

(a) Rotor resistance = 0(b) Rotor reactance at supply

frequency =0(c) Rotor resistance = rotor

reactance at supply frequency (d) Rotor resistance X rotor

reactance at supply frequency

Ans c

119. The P.F of 3Q induction motor is usually

(a) Unity(b) 0.8 loading(c) 0.8 lagging(d) Zero

Ans c

120. How many different speed can be obtained in cased control of two induction motors

(a) 2(b) 4(c) 8(d) 16

Ans b

121. In which of the following case the speed of the induction motor will unchanged


(a) Frequency is doubled of poles reduce to half

(b) Frequency is halfed and no. of pole doubled

(c) Frequency is halfed and no. of pole also halfed

(d) Frequency is doubled and no. of pole remain unultered

Ans c

122. In case of double cage induction motor the inner cage has

(a) Has inductance and low resistance

(b) Low inductance and high resistance

(c) Low inductance and low resistance

(d) High inductance and high resistance

Ans a

123. Locked rotor test on induction motor is conducted to determine

(a) Friction losses(b) Windage losses(c) I2 r losses(d) Core losses

Ans c

124. Open circuit test usually conducted on

(a) Slip ring motor only(b) Wound rotor motor only(c) Either of a or b above(d) None of the above

Ans c

125. The low P.F of induction motor is due to

(a) The reactance lagging magnetizing current necessary to generate the magnetic flux

(b) Stator reactance(c) Rotor leakage reactance(d) All of the above

Ans a

126. Phase advancers are used with induction motor to

(a) Improve power fector(b) Reduce vibration

(c) Reduce copper losses(d) Reduce noise

Ans a

127. During back to back test both machines

(a) Run as induction motors (b) Both machines run as induction

generator(c) One machine run as induction

motor and the other as a induction generator

(d) One machines run as induction motor and the other as a synchronous generator

Ans c

128. During dynamic breaking for induction motor

(a) Fictitious load is applied on motor(a) Stator winding is excited by

direct current(b) Motor is used as induction

generator(c) Stator connections are reversed

Ans b

129. The operation of repeated starting and stopping of an induction motor for exact positioning of the driven equipment is called

(a) Jogging(b) Plugging(c) Balancing(d) Crawling

Ans a

130. A 440 volt, 60 Hz , 3 Q induction motor is to be operated on 50 Hz the desirable supply voltage is

(a) 330 volt(b) 380 volt(c) 400 volt(d) 440 volt

Ans a

131. A stator rotor startic can be used in

(a) Squirrel cage induction motor(b) Slip ring induction motor


(c) Both a and b(d) None of the above

Ans b

132. In moist surrounding which frame of induction motor will be preferred

(a) Drip proof(b) Splash proof(c) Totally inclosed for cooled(d) Open type

Ans c

133. The principle of operation of 3Q induction motor closely resemble to that of, which of the following

(a) D.C series motor(b) Synchronous motor(c) T/F with open circuit secondary(d) T/F with short circuited

secondary

Ans d

134. Under which of the following condition, a squarrel cage induction motor would be preffer over a wound rotor induction motor

(a) When cost is major consideration(b) When higher starting torque is

required(c) When wide range of speed

control is desire(d) When external voltage is to be

necessary introduce into the rotor

Ans a

135. A 3Q induction motor designed to run at 1440 rpm if the rotor motor is replaced by solid iron rotor the rotor speed will be needy


Ans b

136. In a 3Q induction motor when rotor speed is more than the corsponding synchronous speed

(a) The motor run as a generator

(b) The motor act as a synchronous generator

(c) The motor has negative slip(d) The produced torque is more

than rated torque

Ans c

137. When a 3Q induction motor is directly put on line the starting current is usually

(a) 1/5 to 1/7 the full load current(b) ½ to 1/3 of the full load current(c) Same as the full load current(d) 5 to 7 times more than the full

load current

Ans d

138. A 3Q induction motor taken full load current I ampere when power fector is ‘cosQ’ the compound I sinQ will

(a) Equal to copper losses(b) Over cum iron losses(c) Produce magnetism(d) Dissipted as heat

Ans c

139. Which of the following statement is not valid when a squarrel cage induction motor operate under no load

(a) P.F is low(b) Slip is high (c) Rotor current is low(d) Rotor induced e.m.f is low

Ans b

140. A wound rotor induction motor can be distinguished from squirrel cage induction motor by the

(a) Presence of cooling fan(b) Size of motor shaft(c) Presence of slip rings(d) Type of stator

Ans c

141. The rotor of 3Q induction motor receive energy from

(a) 3Q power sorce(b) 1Q power sorce(c) Inverted D.C supply


(d) Stator means of induction or T/F reaction

Ans d

142. When the rotor of a 3Q induction motor runs at synchronous speed, the rotor

(a) E.m.f alone is zero(b) Current torque and e.m.f is zero(c) Current alone is zero(d) Torque alone is zero

Ans b

143. When an induction motor runs at rated current and speed, the iron losses are

(a) Neglizible(b) Very high(c) Independent of supply frequency(d) Independent of supply voltage

Ans a

144. Watt motor reading in no load test on induction motor gives

(a) Copper loss in stator(b) Windage and friction loss(c) Sum of a and b(d) Total loss in the motor on no load

Ans d

145. The power fector (P.F) of a star- connected induction motor is 0.5, on being connected in delta, P.F will

(a) Come zero(b) Remain same(c) Reduce(d) Increase

Ans c

146. The core of rotor of 3Q induction motor

(a) Is always laminated(b) Is always solid(c) Is same time laminated(d) None of these

Ans a

147. What is the advantage of slipring induction motor over the squirrel cage induction motor

(a) It is suitable for high speed(b) Its efficiency(n) is high(c) Its P.F is higher(d) It can be star with help of rotor

resistance

Ans d

148. Which of the following is not a part of a squirrel cage induction motor

(a) Rotor(b) Stator(c) Carbon brush(d) Shaft

Ans c

149. Which of the following lubricants, the shaft of the motor is lubricated

(a) Graphite(b) Grease(c) Silicon oil(d) Mineral oil

Ans b

150. The field of induction motor, rotor with refrance to stator as

(a) Synchronous speed(b) Slip-speed(c) Rotor-speed(d) Very low speed

Ans a

151. The reactance per phase as compare to the resistance per phase of an induction motor is

(a) Quite high(b) Slightly large(c) Almost same(d) Very small

Ans a

152. The torque of induction motor is synchronous-watts is equal to

(a) Rotor out put(b) Stator out put(c) Stator in put(d) Watts at rotor speed

Ans b


153. The shape of torque/slip curve of induction motor is

(a) High parabola(b) State bola(c) State line(d) Rectangular parabola

Ans d

154. When the frequency of rotor of an induction motor is small it can be measured by

(a) Galvano meter(b) D.c moving coil mili voltmeter(c) D.c moving coil am-meter(d) A.c voltmeter

Ans b

155. The stator frame in an induction is used

(a) As a return path for the fluze(b) To hold the armature

stamping/stator(c) To protect the while machine(d) The ventilated the armature

Ans a

156. When ever any poly phase motor is loaded then

(a) Induced e.m.f in the rotor increase and its frequency

(b) Induced e.m.f in the rotor increases and its frequency rises

(c) Induced e.m.f in the rotor is remain constant


Ans a

157. An induction motor crawls at lower speed it is due to

(a) Scrawing(b) Harmonic induction torque(c) High secondary reactance(d) Low secondary reactance

Ans b

158. Semi close stator slots and not slots open slots is used in induction motor

(a) To increase the pull out torque(b) To decrease the slot reactance(c) To decrease magnetizing current(d) None of the above

Ans c

159. In an induction motor scewing of rotor bans reduces

(a) Noise(b) Vibration(c) Sy-cusps(d) All of the above

Ans d

160. In an induction motor the value of average flux density in an air gap should be small

(a) To get good P.F(b) To get poor P.F(c) To achieve good efficiency(d) For minimum cost

Ans a

161. The large no. of slots in an induction motor has

(a) High over load capacity(b) Low over load capacity(c) No effect on over load capacity(d) None of these

Ans a

162. N.E.M.A standard rated motor according to

(a) Frame number(b) Horse power (c) Voltage(d) Weight

Ans a

3 q induction motor

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