250+ TOP MCQs on Reluctance Motor and Answers

Electrical Machines Multiple Choice Questions on “Reluctance Motor”.

1. What is the angle between stator direct axis and quadrature axis?
A. 90°
B. 0°
C. 45°
D. 60°
Answer: A
Clarification: In reluctance motor, direct axis is horizontal axis and quadrature axis is at 90° to the direct axis.

2. Space angle, θ_r is measured between stator d-axis and _______________
A. quadrature axis
B. direct d-axis
C. long rotor axis
D. none of the mentioned
Answer: C
Clarification: Space angle is measured between stator direct axis and long rotor axis.

3. The reluctance offered to the stator flux by two very large air gaps in series with high permeability iron, in reluctance machine is maximum, when the space angle θ_r = ___________
A. 0°
B. 45°
C. 90°
D. 180°
Answer: C
Clarification: Only when θ_r = 90°, the long rotor axis is perpendicular to the stator d-axis, and thus reluctance is maximum.

4. The reluctance offered to the stator flux by two small air gaps in series with high permeability iron, in reluctance machine is minimum, when the space angle θ_r = ___________
A. 0°
B. 45°
C. 90°
D. 270°
Answer: A
Clarification: Only when θ_r = 0°, the long rotor axis is coincident with the stator d-axis, and thus reluctance is minimum.

5. The variation of reluctance Rl with space angle θ_r depends on the shape of __________
A. stator poles
B. rotor poles
C. stator or rotor poles
D. both stator and rotor poles

250+ TOP MCQs on DC Motor Starting and Answers

Answer: D
Clarification: Also, the variation is assumed to be a function of space angle θ_r.

6. Reluctance motor can produce torque at ________
A. any speed less than synchronous speed
B. synchronous speed only
C. any speed greater than synchronous speed
D. all of the mentioned
Answer: B
Clarification: T_e(av) = -1/4 ∅_max²(Rl_q – Rl_d)(1/2 sin⁡(-2δ)), w = synchronous speed
if w_r≠w then T_e(av)=0, and if w_r=w then T_e(av)≠0, as the last term in the equation 1/2 sin⁡(-2δ) does not vary with time, and hence average torque is not equal to zero.

7. For a reluctance motor, the maximum average torque occurs when δ = __________
A. 45°
B. 90°
C. 0°
D. 180°
Answer: A
Clarification: The equation for average torque is T_e(av)=1/8 ∅_max²(Rl_q – Rl_d)sin⁡(2δ), and it is maximum when δ=45°.

8. For a given reluctance motor, Rl_d and Rl_q are ________
A. constant
B. varying
C. zero
D. all of the mentioned
Answer: A
Clarification: Rl_d and Rl_q are constant for a given motor, as they depend on the geometry of the magnetic circuit.

9. The single phase reluctance machine acts as a generator when angle δ is _______
A. positive
B. negative
C. zero
D. any of the mentioned
Answer: B
Clarification: If δ is positive, then the machine acts as a motor and if δ is negative, the machine acts as a generator.

10. Single phase reluctance motors are extensively used in ________
A. grinder applications
B. driving electric clocks and other timing devices
C. welding applications
D. lifts/ elevators

250+ TOP MCQs on Rotating Amplifiers and Answers

Answer: B
Clarification: The single phase reluctance motors operate at constant synchronous speed, in case the supply frequency remains constant, and hence timing devices mostly use these motors.

11. If the salient pole rotor in a single phase reluctance motor is replaced by a cylindrical rotor, then Which of the following statements are true?

A. (i), (ii)
B. (ii), (iii)
C. (iii), (iv)
D. (i), (iv)
Answer: A
Clarification: The reluctance torque is developed only when the reluctance is seen but the stator flux varies with rotor movement, and it depends on the air gap. For a cylindrical rotor, the air gap remains same, and hence no change in reluctance and no torque is developed.

12. Which of the following are applications of singly excited magnetic systems?
A. electromagnets, relays
B. moving-iron instruments
C. reluctance motors
D. all of the mentioned
Answer: D
Clarification: All of the applications mentioned above needs singly excited magnetic systems.

Related Posts