Experiment_13_The_Synchronous_Motor-Part I

Experiment_13_The_Synchronous_Motor-Part I - Experiment 13...

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13 1 Experiment 13 The Synchronous Motor – Part I OBJECTIVE To examine the construction of the 3 Φ synchronous motor. To obtain the starting characteristics of the 3 Φ synchronous motor. DISCUSSION The synchronous motor gets its name from the term synchronous speed, which is the natural speed of the rotating magnetic field of the stator. As you have learned, this natural speed of rotation is controlled strictly by the number of pole pairs and the frequency of the applied power. Like the induction motor, the synchronous motor makes use of the rotating magnetic field. Unlike the induction motor, however, the toque developed does not depend on the induction currents in the rotor. Briefly, the principle of operation of the synchronous motor is as follows. A multiphase source of AC is applied to the stator windings and a rotating magnetic field is produced. A direct current is applied to the rotor windings and a fixed magnetic field is produced. The motor is so constructed that these two magnetic fields react upon each other causing the rotor to rotate at the same speed as the rotating magnetic field. If a load is applied to the rotor shaft, the rotor will momentarily fall behind the rotating field but will continue to rotate at the same synchronous speed. The falling behind is analogous to the rotor being tied to the rotating field with a rubber band. Heavier loads will cause stretching of the band so the rotor position lags the stator field but the rotor continues at the same speed. If the load is made too large, the rotor will pull out of synchronism with the rotating field and, as a result, will no longer rotate at the same speed. The motor is then said to be overloaded. The synchronous motor is not a self-starting motor. The rotor is heavy and from a dead stop it is not possible to bring the rotor into magnetic lock with the rotating magnetic field. For this reason, all synchronous motors have some kind of starting device. A simple starter is another
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13 2 motor which brings the rotor up to approximately 90% of its synchronous speed. The starting
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This note was uploaded on 02/11/2012 for the course EEE 360 taught by Professor Gorur during the Spring '08 term at ASU.

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Experiment_13_The_Synchronous_Motor-Part I - Experiment 13...

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