Electrical Machines
In 3 - Φ induction motor some times copper bars are placed deep in the rotor to

  improve starting torque.
  improve efficiency.
  reduce copper loss.
  improve power factor.

ANSWER DOWNLOAD EXAMIANS APP

Electrical Machines
The synchronous motor can be started by

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

ANSWER DOWNLOAD EXAMIANS APP