Home » Electrical Engineering » Electrical Engineering MCQ » Three Phase Induction Motor

### 1.An induction motor works with

• BAC Only
• CBoth AC & DC
• DNone of these

AC Only

Explanation:

An induction motor works with AC Only.

### 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

Hold the armature stampings in position

Explanation:

The stator frame in an induction motor is used to hold the armature stampings in position.

### 3.The frame of an induction motor is made of

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

Closed grained cast iron

Explanation:

The frame of an induction motor is made of Closed grained cast iron.

### 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

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

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

Consequent pole with opposite polarity

Explanation:

### 7.The induction motor shaft should be

• AHollow
• BStiff
• CFlexible
• DAny of these

Stiff

Explanation:

The induction motor shaft should be Stiff.

### 8.The induction motor shaft is made of

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

Mild steel

Explanation:

The induction motor shaft is made of Mild steel.

### 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

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

Explanation:

Induction motors normally use die cast aluminum rotor because aluminum is Easy to cast owing to its low melting point and is easily available.

### 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

Rotor conductors are short circuited through end rings

Explanation:

In a 3-phase squirrel cage induction motor Rotor conductors are short circuited through end rings.

### 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

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

Facilitate cooling of rotor

Explanation:

The squirrel cage induction motors are provided with blades in order to Facilitate cooling of rotor.

### 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

Three phase winding

Explanation:

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

### 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

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

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

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

External star connected resistors

Explanation:

In a 3-phase slip ring induction motor, brushes are connected to External star connected resistors.

### 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

Rotor at slip rings

Explanation:

In a 3-phase wound rotor induction motor the short circuit gear is used to short circuit the Rotor at slip rings.

### 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

Both (a) and (b)

Explanation:

### 19.A smaller air gap 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

Reduce the magnetizing current

Explanation:

A smaller air gap in a poly phase induction motor helps to Reduce the magnetizing current.

### 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