Electrical Machines - Single Phase Motors

1. If the centrifugal switch of a two-value capacitor motor using two capacitors fails to
open, then
(a) electrolytic capacitor will, in all probability, suffer breakdown
(b) motor will not carry the load
(c) motor will draw excessively high current
(d) motor will not come upto the rated speed.

2. Each of the following statements regarding a shaded-pole motor is true except
(a) its direction of rotation is from un- shaded to shaded portion of the poles
(b) it has very poor efficiency
(c) it has very poor p.f.
(d) it has high starting torque.

3. Compensating winding is employed in an ac series motor in order to
(a) compensate for decrease in field flux
(b) increase the total torque
(c) reduce the sparking at brushes
(d) reduce effects of armature reaction.

4. A universal motor is one which
(a) is available universally
(b) can be marketed internationally
(c) can be operated either on dc or ac supply
(d) runs at dangerously high speed on no-load.

5. In a single-phase series motor the main purpose of inductively-wound compensating winding is to reduce the
(a) reactance emf of commutation
(b) rotational emf of commutation
(c) transformer emf of commutation
(d) none of the above.

6. A repulsion motor is equipped with
(a) a commutator (b) slip-rings
(c) a repeller
(d) neither (a) nor (b).

7. A repulsion-start induction-run single- phase motor runs as an induction motor only when
(a) brushes are shifted to neutral plane
(b) short-circuiter is disconnected
(c) commutator segments are short- circuited
(d) stator winding is reversed.

8. If a dc series motor is operated on ac supply, it will
(a) have poor efficiency
(b) have poor power factor
(c) spark excessively
(d) all of the above
(e) none of the above.

9. An outstanding feature of a universal motor is its
(a) best performance at 50 Hz supply
(b) slow speed at all loads
(c) excellent performance on dc. supply
(d) highest output kW/kg ratio.

10. The direction of rotation of a hysteresis motor is determined by the
(a) retentivity of the rotor material
(b) amount of hysteresis loss
(c) permeability of rotor material
(d) position of shaded pole with respect to the main pole.


    1. a     2.d     3. d     4. c     5. d 
    6. a     7. c     8. d     9. d     10. d


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