Tuesday, September 1, 2020

Chapter 8: Induction Motor- Page 1

  Chapter 8: Induction Motor-

1. The no-load speed of a 3-phase, 4-pole induction motor connected to a 3-phase, 50-Hz supply is expected to be ?rpm.
A.1400
B.1480
C.1450
D.1498


... Answer is (B)

 

 
 

2. A 400-kW, 3-phase, 440-V, 50-Hz induction motor has a speed of 950 r.p.m. on full-load. The machine has 6 poles. The slip of the machine will be
A.0.06
B.0.1
C.0.04
D.0.05

... Answer is (D)

 
 
 

3. In a 34, 4-pole, 50-Hz induction motor running with 1455 rpm, the speed of rotor field with respect to the rotor struc ture is ?rpm.
A. zero
B.1455
C.45
D.1500

... Answer is (C)

 

 
 

4. The effect of increasing the length/id air-gap in an induction motor will be to increase the
A. power factor
B. speed
C. magnetising current
D. air-gap flux

  ... Answer is (C)

 

 
 
5. In a 34 induction motor, reactance under running conditions is less than its standstill value because of decrease in
A. rotor inductance
B. frequency of rotor emf
C. stator magnetic flux
D. mutual flux linking the stator and rotor conductors
  ...
Answer is (B)

 
 
 

6. Under no-load conditions, power factor of an induction motor is about
A. 0.2 lag
B. 0.9 lag
C. unity
D. 0.5 lead

  ... Answer is (A)

 

 
 

7. Which statement regarding double squirrel-cage induction motor (DSCIM) is false?
A. it is particularly useful where frequent starting under heavy loads is required
B. it maintains high efficiency during normal operating conditions
C. it has better speed regulation than single squirrel-cage motor
D. its upper cage is of low resistance and lower cagy of high resistance

... Answer is (D)

 
 

8. The crawling in an induction motor is caused by
A. improper design of the machine
B. low voltage supply
C. high loads
D. harmonics developed in the motor

... Answer is (D)

 
 

9. For starting a Schrage motor, 34 supply is connected to
A. stator as in an ordinary induction motor
B. rotor via slip-rings
C. regulating winding
D. secondary winding via brushes

 
  ... Answer is (B)

 
 

10.  When a Schrage motor runs exactly at synchronous speed, then
A. it behaves, in a sense, like a synchronous motor with compensating winding functioning as dc exciter
B. the speed of the motor field relative to that of the regulating winding becomes zero
C. secondary voltage E2 comes into phase with primary back emf. El.
D. voltage injected from compensating winding into secondary becomes equal and opposite to the secondary induced voltage.

  ... Answer is (A)

 

 

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