The crawling in the induction motor is caused by

Electrical Engineering XYZ MCQs

The crawling in the induction motor is caused by:

  1. High loads
  2. Improper design of stator laminations
  3. Harmonics developed in the motor
  4. Low voltage supply

Correct answer: 3. Harmonics developed in the motor


  • “Crawling” in an induction motor refers to an undesirable phenomenon where the motor runs at very low speeds, much lower than its synchronous speed, even under normal operating conditions.
  • This phenomenon is primarily caused by the presence of harmonics in the motor’s supply voltage.
  • Harmonics are multiples of the fundamental frequency (typically 50 Hz or 60 Hz) and can result from non-linear loads in the electrical system, such as rectifiers, variable frequency drives, or other power electronics.
  • These harmonics distort the sinusoidal waveform of the voltage supplied to the motor, which can lead to unequal distribution of magnetic flux in the motor’s core.
  • The uneven distribution of magnetic flux creates additional magnetic fields in the motor, causing the rotor to experience additional torque components.
  • These torque components can cause the motor to operate at speeds lower than the synchronous speed, resulting in crawling.
  • The other options provided (high loads, improper design of stator laminations, and low voltage supply) may affect the performance of the motor but are not the primary causes of crawling in an induction motor.

Therefore, the correct answer is: Harmonics developed in the motor.

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