Electrical Machines
To have sparkless commutation, the armature reaction effect in a DC machine is neutralized by

 increasing field excitation.
  compensating winding and commutating poles.
 fixing the brush axis inline with the pole axis.
 shifting the brush axis from GNA to MNA.

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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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