Q1. A servomotor is primarily used for:
A) Constant speed operation
B) Precise position control
C) High power transmission
D) Reactive power compensation
Correct Option: B
Explanation: A servomotor is designed for accurate control of position, speed, and torque using a feedback system.
Q2. Which of the following is a DC servomotor?
A) Separately excited DC motor with feedback
B) Squirrel cage induction motor
C) Salient pole synchronous motor
D) Reluctance motor
Correct Option: A
Explanation: A DC servomotor is usually a separately excited DC motor operated in a closed-loop system.
Q3. The main advantage of DC servomotor over AC servomotor is:
A) Low cost
B) Simple construction
C) High torque at low speed
D) Low maintenance
Correct Option: C
Explanation: DC servomotors provide high torque even at very low speeds due to linear torque–current characteristics.
Q4. AC servomotors generally operate on:
A) Single-phase AC supply
B) Three-phase AC supply
C) DC supply
D) Pulsed DC supply
Correct Option: A
Explanation: AC servomotors are typically single-phase or two-phase induction motors.
Q5. Which motor is commonly used in control systems?
A) Induction motor
B) DC shunt motor
C) Servomotor
D) Universal motor
Correct Option: C
Explanation: Servomotors offer fast response, high accuracy, and closed-loop operation.
Q6. For a synchronous motor operating with constant excitation, increase in load causes:
A) Increase in speed
B) Decrease in speed
C) Increase in torque angle
D) Change in excitation current
Correct Option: C
Explanation: Increased load is met by increasing torque angle while speed remains constant.
Q7. In a synchronous motor, speed remains constant because:
A) Rotor current is constant
B) Slip is zero
C) Torque is independent of load
D) Excitation is constant
Correct Option: B
Explanation: Synchronous motor runs at synchronous speed with zero slip.
Q8. Power developed by a cylindrical rotor synchronous motor is:
A) P = EV/Xs sinδ
B) P = VI cosφ
C) P = Tω
D) P = V²/Xs
Correct Option: A
Explanation: Power equation is P = (EV/Xs) sinδ.
Q9. Which component decides the power factor of a synchronous motor?
A) Load
B) Speed
C) Excitation
D) Frequency
Correct Option: C
Explanation: Power factor is controlled by field excitation.
Q10. At unity power factor operation, synchronous motor is said to be:
A) Under-excited
B) Over-excited
C) Normally excited
D) Hunting
Correct Option: C
Explanation: Unity PF occurs at normal excitation.
Q11. Equivalent circuit of synchronous motor resembles:
A) DC motor
B) Transformer
C) Induction motor
D) Alternator
Correct Option: D
Explanation: Circuit is same as alternator with reversed power flow.
Q12. Power flow in synchronous motor is:
A) Electrical → Mechanical → Losses
B) Mechanical → Electrical → Losses
C) Electrical → Losses → Mechanical
D) Electrical → Magnetic → Mechanical
Correct Option: A
Explanation: Electrical power is converted into mechanical power with losses.
Q13. When excitation is increased at constant load:
A) Armature current increases
B) Power factor becomes lagging
C) Power factor becomes leading
D) Speed decreases
Correct Option: C
Explanation: Increasing excitation causes leading power factor operation.
Q14. Effect of increased load with constant excitation is:
A) Increased speed
B) Increased torque angle
C) Reduced armature current
D) Reduced excitation current
Correct Option: B
Explanation: Load increase is met by increase in torque angle δ.
Q15. Hunting in synchronous motor is caused by:
A) Sudden load changes
B) Over-excitation
C) Under-excitation
D) Armature resistance
Correct Option: A
Explanation: Sudden load changes cause oscillations of rotor.
Q16. A 3-phase synchronous motor draws constant excitation. If load is increased, which parameter changes?
A) Speed
B) Rotor current
C) Torque angle
D) Frequency
Correct Option: C
Explanation: Torque angle increases while speed and frequency remain constant.
Q17. If torque angle δ increases from 30° to 60°, power will:
A) Decrease
B) Remain same
C) Increase
D) Become zero
Correct Option: C
Explanation: Power ∝ sinδ, so increase in δ increases power.
Q18. At constant load, increasing excitation causes armature current to:
A) Increase continuously
B) Decrease then increase
C) Increase then decrease
D) Remain constant
Correct Option: B
Explanation: This forms the V-curve characteristic.
Q19. V-curve of synchronous motor represents variation of:
A) Speed vs Load
B) Current vs Load
C) Armature current vs Excitation
D) Power vs Speed
Correct Option: C
Explanation: V-curve shows armature current variation with excitation.
Q20. For maximum power developed in synchronous motor, torque angle δ is:
A) 30°
B) 45°
C) 60°
D) 90°
Correct Option: D
Explanation: Maximum power occurs when sinδ is maximum, i.e., δ = 90°.