Which of the following statements is correct regarding induction motor?

Question

Which of the following statements is correct regarding induction motor?

1. A. The power factor of a 1-phase induction motor is high, while the power factor of a 3-phase induction motor is low
2. B. 1-phase induction motors produce low starting torque, whereas 3-phase induction motors produce high starting torque (Correct answer)
3. C. The efficiency of a 1-phase induction motor is more as compared to a 3-phase induction motor
4. D. All options A, B and C are correct

Correct Answer

Option B — 1-phase induction motors produce low starting torque, whereas 3-phase induction motors produce high starting torque

Detailed Solution & Explanation

The correct answer is 1-phase induction motors produce low starting torque, whereas 3-phase induction motors produce high starting torque.

Key Points

• A single-phase induction motor is not self-starting: its single winding produces a pulsating rather than a rotating magnetic field, so it develops no starting torque without auxiliary means.
• A three-phase induction motor produces a genuinely rotating magnetic field and is therefore self-starting with good starting torque.
• The other options invert the truth: three-phase motors have better power factor and higher efficiency than single-phase machines of comparable rating.

Additional Information

• Single-phase motors are started using a capacitor-start, split-phase or shaded-pole arrangement, all of which create an artificial phase difference to get the rotor turning.
• This is why single-phase motors are confined to small domestic loads — fans, pumps, refrigerators — while industrial drives are almost always three-phase.