COGGING & MAGNETIC LOCK
SQUIRREL CAGE motor sometime s could
not be start, the rotor of squirrel cage motor refuse to start at all,
particularly when the voltage is low. This happen due to Magnetic Locking
between stator and rotor teeth, when number of stator teeth is equal to number
of rotor teeth.
For that Kind of reason sometimes
this phenomenon is call TEETH LOCKING.
It is found that the reluctance of
the magnetic path is minimum when the stator and rotor teeth face to face each
other rather than when teeth of one element (rotor or stator) are
opposite to the slots on the other. It is in such position of minimum
reluctance, that the rotor tends to remain fixed and for that cause serious
trouble during starting.
How to overcome from COGGING:
Cogging of squirrel cage motors can
easily overcome by making the number of rotor slot prime to the number of
stator slots.
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