Answer / romesh roy nigam

Cogging - The rotar of squirral cage motar some times
refuse to start at all,particularly when the voltage is low
this when number of rotar teeth becomes equal to numbers of
stator teeth & due to magnatic locking between stator and
rotar teeth.
Crawling - The phenomenon when squirral cage motar some
times showing tendency to run stably at speed as low as one
seventh of its synchronus speed

Answer / raul

COGGING : when the stator and rotor poles of a 3-phase
Induction motor r either equal or have an integral
ratio......there is a strong alignment or magnetic locking
b/w the stator n rotor teeths.......so due to this the
motor is unable to start inspite of applying full rated
voltage across the motor........
CRAWLING : it is inability of a 3-phase induction motor to
speed up to desired slip speed and has a tendency to run at
a stable speed of 1/7th of the synchronous speed. this
normally occurs due to the 7th harmonic present in the non-
sinusoidal flux wave.......it can be avoided by using short
chorded windings.......

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