Speed Control of DC Motor MCQs – SSC JE Electrical PDF
Which method is used to control the speed of a DC shunt motor above its rated speed? A. Armature resistance control B. Field weakening method C. Voltage control method D. Ward Leonard method Answer: B Explanation: Field weakening (reducing field current) decreases flux, increasing speed. This allows control above rated speed.
Which of the following speed control methods is most suitable for constant torque applications? A. Field control B. Armature resistance control C. Voltage control D. None of the above Answer: B Explanation: Armature resistance control is suitable for constant torque loads but results in poor efficiency.
In Ward Leonard speed control system, the motor used to control speed is: A. Induction motor B. DC compound motor C. DC shunt motor D. Stepper motor Answer: C Explanation: In the Ward Leonard method, a DC shunt motor is used as the drive motor for fine speed control.
Which method gives the widest range of speed control in DC motors? A. Armature control B. Field control C. Ward Leonard system D. Voltage divider method Answer: C Explanation: Ward Leonard system provides smooth and wide speed control from zero to above rated speed.
In armature control method, what happens to the speed of DC motor with increasing load? A. Increases B. Decreases C. Remains constant D. Varies randomly Answer: B Explanation: In armature resistance method, the voltage across armature drops with load, reducing speed.
Field control method is used to: A. Decrease the speed below rated B. Increase the speed above rated C. Maintain constant speed D. Reverse the motor direction Answer: B Explanation: Reducing field flux increases motor speed, hence used to increase speed above rated.
Which of the following is not a method of speed control of DC motors? A. Armature voltage control B. Rotor resistance control C. Field flux control D. Ward Leonard system Answer: B Explanation: Rotor resistance control is used in induction motors, not DC motors.
Which method of speed control is used for precise speed regulation? A. Armature resistance control B. Field control C. Voltage control using rectifiers D. Ward Leonard method Answer: D Explanation: Ward Leonard offers precise and stepless speed control for DC motors.
In field control method, the speed of DC motor is: A. Directly proportional to flux B. Inversely proportional to flux C. Independent of flux D. Proportional to square of flux Answer: B Explanation: Speed is inversely proportional to field flux (N ∝ 1/Φ).
Which method of speed control results in poor efficiency? A. Ward Leonard B. Field weakening C. Armature resistance control D. Voltage control Answer: C Explanation: Armature resistance control causes power loss in resistor, reducing efficiency.
Advanced MCQs on Speed Control of DC Motor – SSC JE
In the Ward Leonard system, which of the following devices is used to vary the voltage applied to the motor? A. Tap changing transformer B. Variable resistor C. Excitation of generator D. Inverter Answer: C Explanation: In the Ward Leonard system, varying the field excitation of the generator controls the output voltage, and hence the motor speed.
The speed of a DC motor can be increased by: A. Increasing the armature resistance B. Decreasing applied voltage C. Increasing field flux D. Decreasing field flux Answer: D Explanation: Speed is inversely proportional to the flux. Reducing flux increases speed.
Which speed control method of DC series motor is suitable for traction applications? A. Armature voltage control B. Field divergence method C. Series-parallel control D. Buck-boost converter Answer: C Explanation: Series-parallel control is widely used in electric traction for controlling speed in series motors.
Which method is not used for controlling the speed of DC shunt motors? A. Field control B. Armature control C. Voltage control D. Cascade control Answer: D Explanation: Cascade control is applicable to induction motors, not to DC motors.
Why is armature resistance control rarely used in DC motors for continuous operation? A. It increases torque B. It reduces efficiency due to power loss C. It causes overspeed D. It increases back EMF Answer: B Explanation: Armature resistance causes I²R losses, leading to low efficiency and heating.
What is the major limitation of field control method for speed control? A. Only below rated speed is possible B. Causes overheating of armature C. Only above rated speed is possible D. Poor speed regulation Answer: C Explanation: Field control method only allows speed control above rated speed and cannot be used to reduce speed below rated.
Which is the most energy-efficient method of DC motor speed control? A. Armature resistance B. Voltage control C. Field control D. Ward Leonard Answer: B Explanation: Voltage control does not involve resistive losses, hence it's more efficient.
In the Rheostatic armature control method, what is added in series with the armature? A. Capacitor B. Inductor C. Resistor D. Diode Answer: C Explanation: A resistor is added to drop part of the applied voltage and reduce armature voltage.
Which one of the following affects the torque-speed characteristic of a DC motor significantly? A. Brush material B. Commutator size C. Speed control method D. Shaft alignment Answer: C Explanation: The method of speed control changes the operating voltage or flux, affecting torque-speed characteristics.
For regenerative braking of a DC shunt motor, the condition required is: A. Supply voltage > Back EMF B. Supply voltage = Back EMF C. Back EMF > Supply voltage D. Armature current = zero Answer: C Explanation: In regenerative braking, the back EMF must be greater than the supply voltage so that the motor feeds power back to the supply.
🎯 Speed Control of DC Motor PYQs – SSC JE (2015–2024)
SSC JE 24-Jan-2018 (Evening Shift) Which method is used to control the speed of a DC shunt motor above rated speed? A. Armature resistance control B. Field weakening method C. Voltage control method D. Ward Leonard method Answer: B Explanation: Speed of a DC shunt motor is inversely proportional to flux (N ∝ 1/Φ). Field weakening reduces flux and increases speed above rated.
SSC JE 27-Jan-2018 (Morning Shift) Which of the following method is suitable for speed control of DC series motor? A. Field diverter method B. Armature voltage control C. Series-parallel control D. Ward Leonard Answer: C Explanation: Series-parallel control is widely used for traction systems using DC series motors.
SSC JE 22-Jan-2018 (Morning Shift) In Ward Leonard system, the speed control of DC motor is achieved by varying: A. Armature current B. Field current of motor C. Output voltage of generator D. Resistance in armature circuit Answer: C Explanation: In the Ward Leonard method, a motor-generator set is used where the output voltage of the generator is controlled to vary the motor speed.
SSC JE 25-Jan-2018 (Afternoon Shift) What happens to the speed of a DC motor if armature resistance is increased? A. Speed increases B. Speed decreases C. Remains constant D. First increases then decreases Answer: B Explanation: Increasing armature resistance causes a voltage drop, reducing effective voltage and hence decreasing speed.
SSC JE 24-Mar-2021 (Shift 1) Which of the following methods gives smooth and wide speed control of DC motor? A. Field control B. Armature control C. Voltage divider D. Ward Leonard method Answer: D Explanation: Ward Leonard system offers fine and stepless speed control from zero to above rated speed.
SSC JE 23-Mar-2021 (Shift 2) Which method of speed control leads to high energy loss and is inefficient? A. Field control B. Armature resistance control C. Voltage control D. Thyristor control Answer: B Explanation: Armature resistance control dissipates power as heat in series resistance, making it inefficient.
SSC JE 29-Oct-2020 (Shift 2) Which component is used in the field control method to adjust the speed of a DC motor? A. Capacitor B. Rheostat C. Rectifier D. Diode Answer: B Explanation: A rheostat is connected in series with the field winding to vary the field current and control motor speed.
