Q1. The principle of torque production in a Switched Reluctance Motor is based on:
A) Interaction of stator and rotor magnetic fields
B) Lorentz force law
C) Tendency of rotor to move towards minimum reluctance
D) Electromagnetic induction
Correct Option: C
Explanation: SR motor operates on the principle of minimum reluctance. When a stator phase is energized, the rotor moves to a position of minimum magnetic reluctance. There is no rotor current and no mutual field interaction.
Q2. Which of the following best describes the rotor construction of an SR motor?
A) Permanent magnet rotor
B) Squirrel cage rotor
C) Salient pole laminated steel rotor without windings
D) Wound field rotor
Correct Option: C
Explanation: The SR motor rotor is made of laminated silicon steel with salient poles and has no windings or magnets.
Q3. In an SR motor, torque is produced when:
A) Rotor flux is maximum
B) Rotor moves from aligned to unaligned position
C) Rotor moves from unaligned to aligned position
D) Current is zero
Correct Option: C
Explanation: Positive torque is produced only when phase inductance increases, i.e., when the rotor moves from unaligned to aligned position.
Q4. Which component is essential for SR motor operation?
A) Slip rings
B) Mechanical commutator
C) Power electronic converter
D) Capacitor
Correct Option: C
Explanation: SR motors require electronic switching of stator phases synchronized with rotor position.
Q5. Which statement about SR motor is TRUE?
A) Rotor carries current
B) Stator and rotor both have windings
C) Rotor position sensor is not required
D) Torque depends on change of inductance with position
Correct Option: D
Explanation: SR motor torque depends on variation of phase inductance with rotor position.
Q6. The torque equation of an SR motor is given by:
A) T = P/ω
B) T = 1/2 i² (dL/dθ)
C) T = BIlr
D) T = E/ω
Correct Option: B
Explanation: Torque is proportional to square of current and rate of change of inductance with rotor position.
Q7. In an SR motor, the inductance of a phase is maximum when the rotor is:
A) Unaligned
B) Partially aligned
C) Fully aligned with stator poles
D) Stationary
Correct Option: C
Explanation: Inductance is maximum at full alignment due to minimum magnetic reluctance.
Q8. Which of the following is an advantage of SR motor?
A) High power factor
B) Simple and rugged construction
C) Low torque ripple
D) Low acoustic noise
Correct Option: B
Explanation: SR motors have simple, rugged rotor construction without windings or magnets.
Q9. The major drawback of SR motor is:
A) Low efficiency
B) High starting current
C) Torque ripple and acoustic noise
D) Poor speed control
Correct Option: C
Explanation: Abrupt phase switching and doubly salient structure cause torque ripple and noise.
Q10. Which motor does not require rotor windings or magnets?
A) Induction motor
B) Synchronous motor
C) Switched reluctance motor
D) DC shunt motor
Correct Option: C
Explanation: SR motor produces torque purely due to reluctance effect.
Q11. Which motor operates on discrete step motion?
A) SR motor
B) Induction motor
C) VR Stepper motor
D) DC motor
Correct Option: C
Explanation: VR Stepper motor rotates in discrete angular steps.
Q12. VR Stepper motor is mainly used for:
A) High-speed drives
B) Continuous rotation applications
C) Precise position control
D) High power applications
Correct Option: C
Explanation: VR Stepper motors are ideal for accurate position control.
Q13. Which motor requires closed-loop control for proper operation?
A) VR Stepper motor
B) SR motor
C) Both
D) None
Correct Option: B
Explanation: SR motor requires rotor position sensing and closed-loop control.
Q14. Compared to VR Stepper motor, SR motor generally operates at:
A) Lower speed
B) Lower power
C) Higher speed and power
D) Same speed
Correct Option: C
Explanation: SR motors are suitable for higher speed and power applications.
Q15. Which motor has higher torque ripple?
A) VR Stepper motor
B) SR motor
C) Both same
D) Depends on supply
Correct Option: B
Explanation: SR motor has higher torque ripple due to abrupt switching.
Q16. In an SR motor, phase inductance increases from 10 mH to 30 mH over a rotor displacement of 20°. If phase current is 5 A, calculate average torque.
A) 0.39 Nm
B) 0.716 Nm
C) 1.56 Nm
D) 3.12 Nm
Correct Option: B
Explanation: Using T = 1/2 i² (ΔL/Δθ), average torque ≈ 0.716 Nm.
Q17. Which of the following torque components exists in SR motor?
A) Mutual torque only
B) Reluctance torque only
C) Electromagnetic torque only
D) Hysteresis torque
Correct Option: B
Explanation: SR motor produces only reluctance torque.
Q18. If dL/dθ < 0 in SR motor and current is positive, torque will be:
A) Positive
B) Negative
C) Zero
D) Infinite
Correct Option: B
Explanation: Negative dL/dθ results in negative torque, producing braking action.
Q19. Compared to VR Stepper motor, SR motor has:
A) Lower efficiency
B) Better high-speed performance
C) Lower power density
D) More complex rotor
Correct Option: B
Explanation: SR motors perform better at high speed and high power ratings.
Q20. Which statement is INCORRECT?
A) SR motor torque depends on inductance variation
B) VR Stepper motor has continuous rotation
C) SR motor requires electronic switching
D) VR Stepper motor operates in steps
Correct Option: B
Explanation: VR Stepper motor operates in discrete steps, not continuous rotation.