Electrical Machines
The synchronous motor can be started by

  coupling it with a DC compound motor.
  providing damper winding in its rotor circuit.
  coupling it with a small AC induction motor called the pony motor.
  any of the above methods.

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Electrical Machines
In speed control of DC Series motor, speed lower than the rated speed can be obtained by

 Connecting an additional resistance in the armature circuit.
 Any of the above.
 Connecting an additional resistance in stator circuit.
 Connecting an additional resistance in the field circuit.

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Electrical Machines
If the applied voltage of a certain transformer is increased by 50% and the frequency is reduced by 50%, the maximum flux density will (assuming that the magnetic circuit remains unsaturated)

 changes to 0.5 times the original value
 remain the same as the original
 changes to 1.5 times the original value
 changes to three times the original value

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