Electrical Machines
A large series motor is never started without some mechanical load on it because otherwise it will

 produce sparking at brushes.
 develop excessive speed and damage itself.
 open fuse or circuit breaker.
 draw too much current.

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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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