Electrical Machines
An ideal synchronous motor has no starting torque because

 relative velocity between the stator and rotor mmf’s is zero.
 rotor winding is highly reactive.
  relative velocity between stator and rotor mmf’s is not zero.
 rotor is made up of salient poles.

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Electrical Machines
Armature reaction in a DC machine

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

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