Electrical Machines
The 3 - Φ induction motors are, by a very considerable margin, the most widely used AC motors as

  they are capable of operation under range of leading and lagging pf.
  these are cheaper in cost, simple and rugged in construction.
  they have very good speed regulation.
  they have maximum efficiency and maximum starting torque.

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Electrical Machines
Cogging in induction motor occurs when

 number of stator teeth - number of rotor teeth = negative number.
 number of stator teeth - number of rotor teeth = even number.
 number of stator teeth - number of rotor teeth = 0.
 number of stator teeth - number of rotor teeth = odd number.

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