Question

Why does synchronous motor is not self-starting? And What techniques are available to start a synchronous motor? (Full Answer)

Answer 1

When the stator of the motor is switched on,the stator flux starts revolving at synchronous speed but the rotor that is excited fails to catch up to a high speed and it begins to vibrate about its mean position and hence the synchronous motors are not self starting.

The techniques are-

1.) Damper winding-When the stator flux is rotating at synchronous speed it cuts the damper winding and an emf is induced and due to the ends being short circuited a current begins to flow which produces a torque and motor starts.

2.) Variable frequency starting-In this method we start with low frequency keeping V/f constant so that flux is constant and frequency can be increased gradually so that it catches up with stator magnetic field.

3.) No load starting-In this method we use auxillary motor which is mechanically coupled to synchronous motor.Auxillary motor can be an induction or dc motor.