Electrical Engineering ⇒ Topic : Principle of synchronous motor
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David
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PRINCIPLE OF OPERATION 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 where Ns (in r.p.m.), f and p are synchronours speed, frequency and number of poles respectively. 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 suirrel-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 sychronous motor accelerates to about 85 to 97% of synchronous speed when started as an induction motor with amortisseur windings. The field circuit is 710W 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. Fig.(a). shows the locking of rotor field poles with unlike poles of stator field. The rotor then runs at the same 'speed as that of the stator field, i.e., Ns.
Fig.(a). Operating principle of a synchronous motor | |
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