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Synchronous motor has zero slip under usual operating condition contrary to induction motor which must slip to produce torque. Synchronous motor is like an induction motor except the rotor is excited by DC field.
Following are the method used for starting of synchronous motor:
Damper windings- These windings are fixed on the salient pole of the rotor so as to start the synchronous motor as induction motor.
Pony motor-The pony motor is an induction which drives the rotor of synchronous motor. Once the speed reaches the synchronous speed, the pony motor is decoupled and synchronous motor runs on its own.
By using variable frequency-Synchronous motor can be started by supplying a reduced frequency to the stator winding.
1) Reducing the speed of stator magnetic field by reducing frequency (using VFD).
2) Using external prime mover to speed up rotor (using an Auxillary motor or pony motor).
3) Using damper or amortisseur windings.
this subject very wide....
starting of those motors are expeinsive and need DC supply where first we shall supply the rotator then supply the stator , there is old ways and moder one
one of modern is by changing the frequency from zero to nominal value
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