# Design of Electrical Machines Questions and Answers – Pulsation Losses & Types of Leakages

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

1. What happens in the rotating electrical machine?
a) armatures are slotted
b) armatures are slotted and results in the movement of rotor
c) the rotor remains stationary
d) the rotor slots are rotating

Explanation: In the rotating electrical machine, the armatures are slotted and there is movement of rotor. Due to the movement of the rotor there are rapid changes of local gap reluctance.

2. What is pulsation losses?
a) flux pulsations are caused due to the slotted armature
b) flux pulsations are caused due to the rotation of machine
c) flux pulsation occurs due to rotor slots are rotating
d) flux pulsations occur due to the change in reluctance

Explanation: In the rotating electrical machine, the armatures are slotted and there is movement of rotor which leads to changes of local gap reluctance. This change leads to flux pulsations which causes additional losses called pulsating losses.

3. In which machine part/parts does the pulsation loss occurs?
a) teeth
b) pole face
c) conductors
d) teeth and pole faces

Explanation: The pulsation losses occurs in the teeth of the machine. The pulsation losses also occur in the pole faces.

4. How are the pulsation losses aggravated?
a) if the air gap is small compared with slot openings
b) if the air gap is reduced
c) if the air gap is increased
d) if the air gap is made larger than the slot openings

Explanation: The pulsation losses occurs in the pole faces and teeth. The pulsation losses are aggravated if the air gap is small compared with slot openings.

5. The slotting produces harmonic fields which cause high frequency losses near the gap surface.
a) true
b) false

Explanation: The pulsation losses are aggravated if the length of air gap is small than the slot openings. The slotting produces harmonic fields which cause high frequency losses near the gap surface.
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6. In which machine is the pulsation losses considerable?
a) synchronous motors
b) induction motors
c) dc shunt motors
d) dc series motors

Explanation: The pulsation losses are aggravated if the length of air gap is small than the slot openings. The pulsation losses although are considerable in the induction motors.

7. What are the factors the permeance depends upon in the zigzag leakage?
a) relative position of stator
b) relative position of rotor
c) relative position of stator and rotor
d) stored energy at any position

Explanation: The permeance for the path of zigzag leakage will depend upon the relative position of stator. The permeance for the path of zigzag leakage will depend upon the relative position of rotor.

8. What is the formula for the stored energy at any position?
a) stored energy at any position = mmf per slot2 * permeance in a particular position
b) stored energy at any position = 2 * mmf per slot2 * permeance in a particular position
c) stored energy at any position = 1/2 * mmf per slot2 * permeance in a particular position
d) stored energy at any position = 1/3 * mmf per slot2 * permeance in a particular position

Explanation: First the mmf per slot along with the permeance in a particular position is calculated. On substitution, the stored energy at any position is calculated.

9. What is the formula for the zigzag permeance?
a) zigzag permeance = average width of the rotor tooth / (1/2 * mmf per slot2)
b) zigzag permeance = average width of the rotor tooth * (1/2 * mmf per slot2)
c) zigzag permeance = 1/average width of the rotor tooth *(1/2 * mmf per slot2)
d) zigzag permeance = average width of the rotor tooth *(1/2 / mmf per slot2)

Explanation: The average width of the rotor tooth is first calculated along with the mmf per slot. On substitution, the zigzag permeance is found out.

10. What is the formula of the zigzag specific permeance?
a) zigzag specific permeance = average width of the rotor tooth * length / (1/2 * mmf per slot2)
b) zigzag specific permeance = average width of the rotor tooth / length * (1/2 * mmf per slot2)
c) zigzag specific permeance = average width of the rotor tooth * length * (1/2 * mmf per slot2)
d) zigzag specific permeance =1/ average width of the rotor tooth * length * (1/2 * mmf per slot2)

Explanation: The average width of the rotor tooth along with the length and mmf per slot is calculated. On substitution the zigzag specific permeance is obtained.

11. What are the factors the overhang leakage reactance is obtained?
a) length of the overhang
b) diameter of the overhang
c) shape of the overhang
d) length of the overhang along with the shape of the overhang

Explanation: The overhang leakage reactance depends upon the length of the overhang. It also depends upon the shape of the overhang.

12. The overhang leakage reactance depends on the degree of saturation in the ferromagnetic parts.
a) true
b) false

Explanation: The overhang leakage reactance depends on the length of the overhang and the shape of the overhang. The overhang leakage reactance also depends upon the degree of saturation in the ferromagnetic parts.

13. What is the relation between the overhang specific permeance and the slot pitch?
a) overhang specific permeance is directly proportional to the slot pitch
b) overhang specific permeance is indirectly proportional to the slot pitch
c) overhang specific permeance is directly proportional to the square of the slot pitch
d) overhang specific permeance is indirectly proportional to the square of the slot pitch

Explanation: The overhang specific permeance relation obtained is an empirical relation. In the empirical relation, the overhang specific permeance is indirectly proportional to the slot pitch.

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