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

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

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Electrical Machines
Armature reaction in a DC machine

 is in the same direction as the main poles.
  makes an angle of 90° with the main pole axis.
 is in direct opposition to the main poles.
 makes an angle with the main pole axis which is load dependent.

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