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

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

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Electrical Machines
An ideal synchronous motor has no starting torque because

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

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