Operating Principle of Synchronous Motor
Synchronous Motor :
The motor which runs at synchronous speed is known as the synchronous motor. The synchronous speed means the constant speed at which the motor generates the electromotive force. The motor is used for converting the electrical energy into mechanical energy.
This article is all about of operating principle of Synchronous Motor. After learning construction of Synchronous Motor, the principle of operations of Synchronous Motor is necessary to learn, so we can easily understand the working of Synchronous Motor.
 |
Operating Principle of Synchronous Motor |
When the stator windings of a 3-phase synchronous motor are supplied with rated 3-phase voltage, a rotating field travelling at synchronous speed is set up.
The synchronous speed is found from the relation
Ns = 120f / P
where, Ns = synchronous speed
f = frequency
P = No. Of poles
This rotating magnetic field cuts across the amortisseur or squirrel-cage winding of the rotor and induces voltages and currents in the bars of this winding.
The resultant magnetic field of squirrel-cage winding embedded in the rotor field poles reacts with the stator field in such a manner as to cause the rotation of the motor.
The rotor will increase its speed to a point slightly below the synchronous speed of the stator field.
The rotor of the typical synchronous motor accelerates to about 85 to 97% of synchronous speed when started as an induction motor with amortisseur windings.
The field circuit is now excited from an outside source of D.C. and magnetic poles of fixed polarity are set up in the rotor field cores.
The fixed magnetic poles of the rotor are attracted to unlike poles of the rotating magnetic field set up by the stator windings.
The rotor, then runs at the same speed as that of the stator field, i.e., Ns.
