what is cogging and crawling

Answer Posted / pugezhenthi.p

The cogging effect is the attraction between the magnets and
the stator poles when at rest; this attraction and cogging
is easily felt when trying to turn an electric motor by
hand. The rotor resists the turning, the magnets attempting
to stay bonded to the current poles, until just over halfway
through the air gap, where the attraction to the next pole
is stronger than that of the previous pole, resulting in a
"clunking" or jumping effect at low RPM (such as when trying
to turn by hand). This is the cogging effect, resulting in a
large torque required to begin rotation.
The motor runs at one seventh of the synchronous speed if
the full rated supply voltage is applied is known as
crawling. This is happens because of 7th harmonic induction
torque

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