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Three Phase Induction Motor MCQ Question & Answer

1.An induction motor works with

  • ADC only
  • BAC Only 
  • CBoth AC & DC
  • DNone of these
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Answer:

AC Only 

Explanation:

2.The stator frame in an induction motor is used to

  • AHold the armature stampings in position
  • BVentilate the armature
  • CProtect the whole machine
  • DProvide return path for the flux
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Answer:

Hold the armature stampings in position

Explanation:

3.The frame of an induction motor is made of

  • AAluminum
  • BSilicon steel
  • CClosed grained cast iron
  • DStainless steel
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Answer:

Closed grained cast iron

Explanation:

4.The stator core of a 3- phase induction motor is laminated in order to reduce the

  • AEddy current loss
  • BHysteresis loss
  • CBoth eddy current and hysteresis I loss
  • DWeight of the stator
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Answer:

Eddy current loss

Explanation:

5.Use of fractional pitch winding

  • AResults in reduced leakage reactance
  • BResults in reduced axial length of the machine
  • CMakes it stiffer
  • DAll of the above
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Answer:

All of the above

Explanation:

6.If all the stator coils of an induction motor are connected for the same magnetic polarity, there will be formed an equal number of

  • ARotor poles with same polarity
  • BRotor poles with opposite polarity
  • CConsequent pole with opposite polarity
  • DConsequent poles with same polarity
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Answer:

Consequent pole with opposite polarity

Explanation:

7.The induction motor shaft should be

  • AHollow
  • BStiff
  • CFlexible
  • DAny of these
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Answer:

Stiff

Explanation:

8.The induction motor shaft is made of

  • AMild steel
  • BCast iron
  • CHigh speed steel
  • DStainless steel
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Answer:

Mild steel

Explanation:

9.Induction motors normally use die cast aluminum rotor because aluminum is

  • ACheaper in cost
  • BLighter in weight
  • CEasy to cast owing to its low melting point and is easily available
  • DOf low resistivity
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Answer:

Easy to cast owing to its low melting point and is easily available

Explanation:

10.In a 3-phase squirrel cage induction motor

  • ARotor conductors are short circuited through end rings
  • BRotor conductor ends are short circuited through slip rings
  • CRotor conductors are kept open
  • DNone of the above
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Answer:

Rotor conductors are short circuited through end rings

Explanation:

11.The squirrel cage rotor of a 6-pole induction motor can be used for ____induction motor

  • AOnly 6-pole
  • B6 or 12 poles
  • CAny number of poles in an
  • DNone of the above
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Answer:

Any number of poles in an

Explanation:

12.The squirrel cage induction motors are provided with blades in order to

  • AFacilitate cooling of rotor
  • BBalance the rotor dynamically
  • CEliminate noise
  • DNone of these
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Answer:

Facilitate cooling of rotor

Explanation:

13.The rotor of a 3-phase wound rotor induction motor is provided with

  • ASingle phase winding
  • BThree phase winding
  • CHeavy copper or aluminum bars placed in rotor slots
  • DHeavy short-circuited end rings
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Answer:

Three phase winding

Explanation:

14.In a 3-phase slip ring induction motor, the rotor winding terminals are brought out through slip rings to

  • AConnect extra resistance across them during starting
  • BConnect them either in star or in delta as per need
  • CConnect to 3-phase ac supply
  • DClose the rotor circuit externally
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Answer:

Connect extra resistance across them during starting

Explanation:

15.The rotor winding for a 3-phase slip ring induction motor having delta connected stator must be connected in

  • ADelta
  • BStar
  • CDelta or star according to need
  • DNone of the above
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Answer:

Star

Explanation:

16.In a 3-phase slip ring induction motor, brushes are connected to

  • AExternal star connected resistors
  • BDC supply
  • C3 – Phase AC supply
  • DEqualizing coils
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Answer:

External star connected resistors

Explanation:

17.In a 3-phase wound rotor induction motor the short circuit gear is used to short circuit the

  • AStator phases of the motor
  • BRotor at slip rings
  • CStarting resistance in the starter
  • DNone of the above
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Answer:

Rotor at slip rings

Explanation:

18.Uneven gap in an induction motor is likely to cause

  • AHeating of motor
  • BUnbalancing of motor shaft
  • CBoth (a) and (b)
  • DNone of these
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Answer:

Both (a) and (b)

Explanation:

19.A smaller air gaps in a poly phase induction motor helps to

  • AReduce the chance of crawling
  • BIncrease the starting torque
  • CReduce the chance of cogging
  • DReduce the magnetizing current
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Answer:

Reduce the magnetizing current

Explanation:

20.In an induction motor, if the air gap is increased

  • A Its speed will reduce
  • BIts efficiency will improve
  • CIts power facts will reduce
  • DIts breakdown torque will reduce
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Answer:

Its power facts will reduce

Explanation: