Electrical Machines
An inverted V-curve of synchronous motor shows the variation of

 power factor and supply voltage during hunting
 supply voltage and field current at constant excitation
All of these
 power factor and dc excitation at constant load

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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 have very good speed regulation.
  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.

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