# Design of Electrical Machines Questions and Answers – Types of Motor

This set of Design of Electrical Machines Multiple Choice Questions & Answers (MCQs) focuses on “Types of Motor”.

1. What is the special feature of single phase induction motor?
a) high starting torque
b) low starting torque
c) average starting torque
d) zero starting torque

Explanation: The single phase induction motor has no inherent starting torque. Thus special means should be used to make it self starting.

2. How many methods are present in the self starting of the single phase induction motor?
a) 1
b) 2
c) 3
d) 4

Explanation: There are 3 methods involved in the self starting of the single phase induction motor. They are split phase starting, shaded pole starting, repulsion motor starting.

3. What are the names of the windings used in the split phase starting?
a) starting windings
b) auxiliary windings
c) starting or auxiliary windings
d) starting and auxiliary windings

Explanation: The single phase induction motor is not self starting. The starting or auxiliary windings are used along with the running or main windings.

4. What is the displacement of the running and the starting windings used?
a) running winding displaces the starting winding by 180°
b) running winding displaces the starting winding by 90°
c) starting winding displaces the running winding by 90°
d) starting winding displaces the running winding by 180°

Explanation: The split phase starting makes use of the starting windings along with the running windings. The running winding displaces the starting windings by 900.

5. How is the required phase displacement between the current in the running and starting windings obtained?
a) by connecting a suitable resistor
b) by connecting a suitable capacitor
c) by connecting a suitable inductor
d) by connecting a suitable impedance

Explanation: The running winding displaces the starting winding by 90°. The required phase displacement is obtained by connecting a suitable impedance in series with any of the windings.
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6. When is the starting winding cut out of the circuit in the split phase motor?
a) when the motor speed reaches 65 % of the full load speed
b) when the motor speed reaches 75 % of the full load speed
c) when the motor speed reaches 50 % of the full load speed
d) when the motor speed reaches 85 % of the full load speed

Explanation: The single phase induction motor is not a self starting machine and hence starting windings are connected in series with the running winding. The starting windings are cut out when the motor speed reaches 75 % of the full load speed.

7. What is the shaded pole starting method?
a) part of the pole is shaded by open circuited copper ring
b) part of the pole is shaded by short circuited copper ring
c) the pole is shaded by open circuited copper ring
d) the pole is shaded by short circuited copper ring

Explanation: One of the starting methods of the single phase induction motor is the shaded pole starting method. Here the part of the pole is shaded by the short circuited copper ring.

8. What happens in the shaded pole starting method according to the displacement?

Explanation: The shaded pole starting method is that the part of the pole is shaded by short circuited copper ring. The displacement between shaded and unshaded portion varies between 200-300.

9. For what type of machines is the shaded pole starting method suitable?
a) for outputs below 60 watt
b) for output below 50 watt
c) for output below 40 watt
d) for output above 50 watt

Explanation: The efficiency of the shaded pole starting method is very low. The shaded pole starting method is used for outputs below 60 watts.

10. When is the repulsion motor starting method used?
a) when low starting torque is required
b) when high starting torque is required
c) when high running torque is required
d) when low running torque is required

Explanation: The repulsion motor starting method is one of the 3 methods of starting the single phase induction motor. It is used when the high starting torque is required.

11. What is the specialty in the repulsion motor starting method?
a) cage winding is replaced by armature windings
b) cage winding is replaced by field windings
c) cage winding is replaced by commutator windings
d) cage winding is replaced by bearings

Explanation: The repulsion motor starting method is one of the methods used in the starting of the single phase induction motor. Here the cage winding is replaced by the commutator windings.

12. What happens in the repulsion motor starting method?
a) the cage windings is dominant
b) the commutator windings are dominant
c) the rotor windings are dominant
d) the stator windings are dominant

Explanation: The repulsion motor starting method is one of the starting methods of single phase induction motor. The commutator windings are dominant and hence gives good starting torque.

13. What is the range of output watt for the shaded pole induction machine?
a) 0.37-50
b) 90-750
c) 90-3700
d) 7.5-370

Explanation: The range of output watt for capacitor type induction motor is 90-750 and that of the repulsion start motor is 90-3700. The range of output watt for resistor type induction motor is 7.5-370 and that of the shaded pole type is 0.37-50.

14. What is the range of the starting current of capacitor type induction motor?
a) 5-7
b) 4–6
c) 2-6
d) 2-3

Explanation: The range of starting current is 5-7 for resistor type induction motor and that of the repulsion start motor is 2-3. The range of the starting current of capacitor induction motor is 4-6.

15. What is the range of the starting torque of shaded pole induction motor?
a) 2-4
b) 2-3.5
c) 0.2-0.3
d) 0.25-0.5

Explanation: The range of starting torque in the capacitor induction motor is 2-3.5 and that of the repulsion start induction motor is 2-4. The range of the starting torque of the shaded pole induction motor is 0.2-0.3.

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