Correct option is A
Crawling in an Induction Motor:
· Crawling refers to a phenomenon in which an induction motor runs at a speed much lower than its synchronous speed, typically at about 1/7th of the synchronous speed.
· This behavior is primarily caused by the presence of harmonics in the supply voltage or the design of the motor itself.
Harmonics:
· In particular, the 7th harmonic in the supply current creates a torque at about 1/7th of the synchronous speed.
· These harmonics produce additional rotating magnetic fields that interfere with the main rotating magnetic field, causing the motor to "crawl" at a subnormal speed.
· Crawling phenomenon occurs only in squirrel cage induction motor.
· Crawling is caused by parallel space harmonic.
· Negative sequence current is generated in unbalanced condition of the motor.
