multiple choice questions on induction machines # 9

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objectives on induction motor 9


1) The torque-slip characteristics of an induction motor is approximately a/an
A) straight line
B) rectangular parabola
C) parabola
D) hyperbola

Ans:B

2) If the rotor circuit resistance is increased in an induction motor, the maximum torque will occur at
A) lower speed
B) high speed
C) the same speed
D) none of these

Ans:A

3) Stable operation of an induction motor is
A) between zero slip and unity slip
B) between 0.5 slip and 0.95 slip
C) between zero slip and slip corresponding to maximum torque
D) between slip corresponding to maximum torque and unity slip

Ans:C

4) The losses that occur in an induction motor are
A) stator copper loss
B) stator iron loss
C) rotor copper loss
D) windage and friction losses
E) all the above

Ans:E

5) In a 3-phase induction motor iron loss mainly occurs in
A) stator and rotor
B) rotor core and rotor teeth
C) stator core and stator teeth
D) stator winding

Ans:C

6) An increase in rotor circuit reactance of a 3-phase induction motor will
A) reduce starting torque as well as maximum torque
B) increase starting torque as well as maximum torque
C) increase starting torque and reduce maximum torque
D) increase maximum torque and reduce starting torque

Ans:A

7) The supply voltage to an induction motor is reduced by 10%. By what percentage approximately will the maximum torque decrease?
A) 50%
B) 10%
C) 20%
D) 40%

Ans:C

8) When the applied voltage per phase is reduced to one-half, the starting torque of a three phase squirrel cage induction motor becomes
A) 1/2 of the initial value
B) 1/4 of the initial value
C) twice of initial value
D) 4 times of initial value

Ans:B

9) In a 3-phase induction motor, the starting torque will be maximum when
A) R2 = 1/X2
B) R2 = X2
C) R2= X2^2
D) R2 = √X2

Ans:B

10) Breakdown torque of a 3-phase induction motor of negligible stator impedance is
A) directly proportional to the rotor resistance
B) inversely proportional to the rotor resistance
C)  directly proportional to the reactance
D) inversely proportional to the rotor leakage reactance

Ans:D

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