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

 supply voltage and excitation current at constant load.
 power factor and supply voltage during hunting.
  power factor and DC excitation at constant load.
 supply voltage and field current at constant excitation.

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Electrical Machines
In dc machines, the field system has to be provided on stator unlike synchronous machines Where in it could be on any member, because

 it reduces field structure iron losses
 it gives more uniform air-gap flux distribution
 dc machines are comparatively low rating machines.
 commutator action is not possible otherwise

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