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Electrical Engineering Objective Questions { Induction Motors }

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.

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

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

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

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

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

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

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