Electrical Machines
Counter emf of a DC motor

 regulates its armature voltage.
 helps in energy conversion.
 exceeds supply voltage
 aids applied voltage.

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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.
  they have maximum efficiency and maximum starting torque.
  these are cheaper in cost, simple and rugged in construction.
  they have very good speed regulation.

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