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

  they have maximum efficiency and maximum starting torque.
  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.

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Electrical Machines
The residual magnetism of a self-excited dc generator is lost. To build up its emf again

 field winding must be excited by low voltage dc supply
 the armature connection must be reversed
 the field winding must be replaced
 the field winding connection must be reversed

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