The phenomenon of ‘crawling’ in a 3-phase induction motor is primarily caused by:
AUnbalanced supply voltage
B3rd time harmonics
C5th space harmonics in the air-gap field
D7th space harmonics in the air-gap field
Explanation
Crawling occurs when the motor runs at approximately 1/7th of its synchronous speed due to strong 7th space harmonic torque produced in the air gap.

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