Free Electrical Machines MCQs with Answers
1,061 Electrical Machines MCQs from Electrical Engineering, each with the correct answer and a written explanation of why it is correct. Free and unlimited, with no account needed.
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- A. Starting voltage is reduced
- B. Starting current is reduced
- C. Both A. and B.
- D. None of the above
Explanation: A star-delta starter initially connects the motor in star, reducing each winding's voltage to 1/√3 of the delta value.
Correct answer: Both A. and B.- A. D.C. motor
- B. Squirrel cage induction motor
- C. Wound rotor induction motor
- D. Synchronous motor
Explanation: A DC motor permits smooth and wide-range speed control through armature voltage, field flux, or both.
Correct answer: D.C. motor- A. Single phase motor
- B. Synchronous motor
- C. A.C. slip ring motor
- D. Ward-Leonard controlled D.C. shunt motor
Explanation: A slip-ring induction motor provides high starting torque and allows useful speed control by adding resistance to the rotor circuit…
Correct answer: A.C. slip ring motor- A. type of drive
- B. span
- C. tonnes
- D. any of the above
Explanation: Crane capacity means the maximum load the crane can safely lift, so it is specified in tonnes.
Correct answer: tonnes25. Which of the following motors is preferred when quick speed reversal is the main consideration ?
- A. Squirrel cage induction motor
- B. Wound rotor induction motor
- C. Synchronous motor
- D. D.C. motor
Explanation: A DC motor can reverse quickly by reversing armature connections or control voltage while retaining strong torque.
Correct answer: D.C. motor- A. Squirel cage induction motor
- B. Schrage motor
- C. Synchronous motor
- D. None of the above
Explanation: A synchronous motor cannot develop starting torque at standstill, so a pony motor first brings its rotor close to synchronous speed.
Correct answer: Synchronous motor- A. Lower cost
- B. Better efficiency
- C. High power factor
- D. All of the above
Explanation: A synchronous motor can operate at a leading power factor by overexciting its field, which improves the power factor of the supply system.
Correct answer: High power factor- A. Synchronous motor
- B. D.C. differentially compound motor
- C. Ward-Leonard controlled D.C. shunt motor
- D. AC. slip ring motor
Explanation: Crane travel requires high starting torque and controlled acceleration, which are provided well by an AC slip-ring induction motor through…
Correct answer: AC. slip ring motor- A. Precise control
- B. Smooth movement
- C. Fast speed control
- D. All of the above
Explanation: Crane hoisting and lowering require precise positioning, smooth movement to avoid load swing, and rapid speed control.
Correct answer: All of the above- A. slop speed operation
- B. high starting torque
- C. low windage losses
- D. all of the above
Explanation: A wound-rotor induction motor allows external resistance to be added to the rotor circuit, producing high starting torque and controlled…
Correct answer: high starting torque- A. ore handling plants
- B. steel plants
- C. heavy engineering workshops
- D. all of the above
Explanation: Heavy-duty cranes are needed wherever very large loads must be lifted and transported, including ore-handling plants, steel plants, and…
Correct answer: all of the above- A. Synchronous motor
- B. Slip ring induction motor
- C. Pole changing induction motor
- D. Squirrel cage induction motor
Explanation: A synchronous motor is preferred for a motor-generator set because it maintains nearly constant speed and can operate at a desired power…
Correct answer: Synchronous motor- A. auto-transformer
- B. star-delta
- C. slip ring
- D. any of the above
Explanation: Star-delta and autotransformer starting reduce the voltage applied to the stator, whereas a slip-ring motor normally receives full stator…
Correct answer: slip ring- A. Exhaust fan
- B. Ceiling fan
- C. Refrigerator
- D. Water pump
Explanation: A ceiling fan commonly uses variable speed so its airflow can be adjusted according to comfort.
Correct answer: Ceiling fan- A. D.C. shunt motor
- B. D.C. series motor
- C. Squirrel cage induction motor
- D. Slip ring induction motor
Explanation: A squirrel-cage induction motor has relatively low starting torque because its rotor resistance is fixed and usually small, giving a low…
Correct answer: Squirrel cage induction motor- A. Electric shovels
- B. Cranes
- C. Rolling mills
- D. All of the above
Explanation: Electric shovels, cranes, and rolling mills all have repeated accelerating, loading, unloading, and braking periods.
Correct answer: All of the above- A. Pole changing squirrel cage motors
- B. D.C. motors with Ward-leonard con-trol
- C. A.C. slip ring motors with variable resistance
- D. Any of the above
Explanation: Derricks and winches require high starting torque and controllable speed, which can be provided by pole-changing motors, Ward-Leonard DC…
Correct answer: Any of the above- A. d.c. shunt motor
- B. schrage motor
- C. synchronous motor
- D. slip ring induction motor
Explanation: A slip-ring induction motor provides access to the rotor circuit through slip rings, allowing an injected EMF to control rotor current and…
Correct answer: slip ring induction motor- A. Slip ring induction motor
- B. Synchronous motor
- C. D.C. shunt motor
- D. Schrage motor
Explanation: A synchronous motor runs at synchronous speed, which is fixed by supply frequency and pole number, so its speed-control range is…
Correct answer: Synchronous motor- A. Resistance in rotor circuit
- B. Resistance in stator circuit
- C. Auto-transformer starting
- D. Star-delta starting
Explanation: A squirrel-cage rotor has no accessible external circuit, so resistance cannot be inserted directly into its rotor circuit.
Correct answer: Resistance in rotor circuit