# Design of Electrical Machines Questions and Answers – Design of a Small Reluctance Motor

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

1. How is the reluctance motor with respect to a synchronous motor and are the field windings?
a) small synchronous motor with field windings
b) small synchronous motor without field windings
c) large synchronous motor with field windings
d) large synchronous motor without field windings

Explanation: Reluctance motor is nothing but a simple small synchronous motor with salient pole rotor. They are without field windings in which the field flux is produced.

2. Why is the three phase reluctance motor preferred over single phase reluctance motor?
a) single phase reluctance motors have the phenomenon of hunting
b) single phase reluctance motors have the phenomenon of over voltage
c) single phase reluctance motors have high losses
d) single phase reluctance motors have low output

Explanation: The reluctance motor is a small synchronous motor with salient pole rotor. The single phase reluctance motors have the phenomenon of hunting.

3. What is the relation of the input voltage with the magnetic flux?
a) if the input voltage is constant, the magnetic flux increases
b) if the input voltage is constant, the magnetic flux decreases
c) if the input voltage is constant, the magnetic flux is constant
d) if the input voltage is constant, the magnetic flux is zero

Explanation: The input voltage is given constant, which results in the constant magnetic flux. The magnetic flux is independent of the excitation.

4. What is the power factor in the reluctance motor and the range of efficiency?
b) lagging power factor, 50-75%
c) zero power factor, 55-80%
d) lagging power factor, 55-75%

Explanation: The power factor in the reluctance motor is lagging power factor. The efficiency of the machine is about 55-75%.

5. What is the angle at which the electromagnetic torque is maximum?
a) 30°
b) 45°
c) 60°
d) 90°

Explanation: The electromagnetic torque is maximum at the angle of 45°. The range of operation of the reluctance motor lies in the range of 0-45°.

6. What is the range of the ratio of the direct axis reactance to the quadrature axis reactance?
a) 1.5-2.3
b) 1.6-2.7
c) 1.6-2.2
d) 1.2-2.0

Explanation: The minimum value of the ratio of the direct axis reactance to the quadrature axis reactance is 1.6. The maximum value of the ratio of the direct axis reactance to the quadrature axis reactance is 2.2.

7. How many design dimension are present in the design of the small reluctance motor?
a) 3
b) 4
c) 5
d) 6

Explanation: There are 5 design dimensions present in the design of the small reluctance motors. They are the design of the main dimensions, design of stator windings, design of the rotor of the reluctance motor, design of performance parameters, design of losses and efficiency.

8. What is the range of the constant used in the calculation of the active power of reluctance motor?
a) 0.3-0.4
b) 0.35-0.55
c) 0.40-0.50
d) 0.35-0.60

Explanation: The minimum value of the range of the constant used in the calculation of the active power of reluctance motor is 0.35. The maximum value of the range of the constant used in the calculation of the active power of reluctance motor is 0.55.

9. How many steps are present in the calculation of the determination of main dimensions?
a) 5
b) 4
c) 3
d) 2

Explanation: There are 5 steps present in the calculation of the determination of main dimensions. They are electromagnetic power of reluctance motor, output coefficient, pole pitch, pole arc, peripheral velocity.

10. How many steps are present in the calculation of the design of stator windings?
a) 10
b) 11
c) 9
d) 12

Explanation: There are 11 steps involved in the calculation of the design of stator windings. They are input current to motor, number of stator slots, stator winding pitch, winding factor, useful flux, number of turns per stator winding, cross sectional area of the stator winding, slot area, mean length for conductor, active resistance of stator winding, specific permeance of leakage flux.

11. How many steps are present in the calculation of the design of rotor of reluctance motors?
a) 4
b) 5
c) 3
d) 2

Explanation: There are 4 steps involved in the design of rotor of reluctance motor. They are rotor diameter calculation, height of rotor core, mmf for magnetic circuit, saturation coefficient of motor.

12. How many steps are involved in the design of performance parameters?
a) 6
b) 5
c) 7
d) 8

Explanation: There are 7 steps involved in the design of the performance parameters. They are no load current, height of steel stator teeth, weight of steel in the stator core, copper loss in the stator winding under no load, active resistance and leakage reactance, active component of no load current, starting torque of 3 phase reluctance motor.

13. How many design steps are involved in the determination of the losses and efficiency?
a) 2
b) 3
c) 4
d) 5

Explanation: There are 3 steps involved in the determination of the losses and efficiency. They are copper loss in stator winding, iron loss in stator steel, mechanical loss in the motor.

14. What is the formula for the slot pitch factor in design of rotors?
a) slot pitch factor = 3.14*rotor diameter*number of rotor slots
b) slot pitch factor = 3.14/rotor diameter*number of rotor slots
c) slot pitch factor = 3.14*rotor diameter/number of rotor slots
d) slot pitch factor = 1/3.14*rotor diameter*number of rotor slots

Explanation: First the rotor diameter and the number of rotor slots are first calculated. On substitution the slot pitch factor can be obtained.

15. The active resistance of the stator winding is calculated at the temperature of 45° C.
a) true
b) false 