The principle of operation of an induction motor is similar to which of the following?
ASynchronous motor
BRepulsion start induction motor
CCapacitor-start induction run
DTransformer with shorted secondary
Electrical Engineering · Question Bank
3P Induction Motors
115 of 135 questions match · page 4 of 6. Answer in your head first, then check the solution.
Which one is true about the torque developed by a three-phase induction motor?
AIt is directly proportional to the rotor resistance
BIt is directly proportional to the square of the supply voltage
CIt is inversely proportional to the supply voltage
DIt is inversely proportional to the slip
What type of field is produced by the stator of a three-phase induction motor?
ASteady
BSinusoidal
CRotating
DAlternating
Which one is true about an induction motor?
AIt is an essentially constant speed motor
BIt is a variable speed motor
CIt is a very costly motor
DIt is a motor that requires higher maintenance
Which of the following is the source of power of the rotor of an induction motor?
AAC supply voltage
BExternal exciter
CCentrifugal switch
DMagnetic induction
The fractional slip of an induction motor is the ratio of which of the following?
ARotor copper loss to rotor input
BStator copper loss to stator input
CRotor copper loss to rotor output
DRotor copper loss to stator copper loss
Which of the following is a reason why the losses in the rotor of an induction motor are less than the losses in the stator?
ALess rotor frequency
BSlots in the rotor are skewed
CRotor diameter is small
DNone of these
Induction motors now a days use die cast aluminum rotor for which of the following reasons? 1
AAluminum is lighter than copper
BAluminum is cheaper than copper
CAluminum is easy to cast because of its low melting point and easily available
DAluminum has less resistivity than copper
Which type of motors don't have a commutator?
AInduction motor
BShunt motor
CSeries motor
DRepulsion motor
In which of the following starting methods is the starting current maximum?
AAutotransformer starting
BStar-delta starting
CDirect on line starting
DPart winding starting
How is the rotor current of a three-phase induction motor related to the slip of the motor?
ADirectly proportional to the slip
BInversely proportional to the slip
CDirectly proportional to the square of the slip
DInversely proportional to the square of the slip
A three-phase induction motor is running at a slip s (in decimal). What is the approximate efficiency of the rotor?
As
B1 + s
C1 − s
Ds − 1
Which of the following conditions will give maximum voltage to the rotor of an induction motor?
AWhen its rotor is blocked
BWhen it is running at full load condition
CWhen it is running at no-load condition
DWhen it is running at overload condition
Which of the following will reverse the direction of rotation of an induction motor?
AReverse the polarity of the rotor circuit
BUse a reverse power relay
CInterchange all three supply lines
DInterchange any two of the three supply lines
What term refers to the difference between the synchronous speed and the actual rotor speed of an induction motor?
ARegulation
BBack lash
CLag
DSlip
Which statement is not true regarding the skewing of the rotor bars in a squirrel cage induction motor?
AIt prevents cogging
BIt reduces motor hum
CIt will produce uniform torque
DIt increases the starting torque
A wound rotor induction motor is not normally selected on the basis of which of the following reasons?
AHigh starting torque is the main consideration
BVariable speed operation is required
CCost is the main consideration
DAn external voltage is to be fed in the rotor
What will happen to the synchronous speed if the frequency of the 3-phase supply to the stator of an induction motor is increased?
AIt will decrease
BIt will increase
CIt will remain the same
DNone of these
In a three-phase induction motor, the rotor reactance under running condition is less than its value at standstill. This is due to the reduction of which of the following?
ARotor inductance
BNumber of stator poles
CRotor frequency
DRotor resistance
What type of rotor is used by a double cage induction motor?
ASlip-ring type
BSquirrel-cage type
CCommutator type
DCombination of squirrel cage and slip ring types
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