Introduction

In previous chapters we have read that a motional emf is induced when a conductor coil is moved in a constant magnetic field. There must be a relative motion between the steady magnetic field and the conductor to get the generated emf This mechanism is reciprocal. That means we can even get the movement if we apply the emf in the same manner. Thus, we can conclude that a dynamic machine is applied to convert the electrical energy to mechanical energy and vice-versa. We have already come to know about DC machine and induction machine. In DC machine, the single phase power is commutated via a commutator to convert AC to DC and vice-versa. Whereas in induction motor we use a shorted three phase winding as stator winding. An induction machine runs at a speed lesser than the synchronous speed. If we energize the field from a DC source and the armature current is supplied from an AC source the rotor will rotate at exactly the same speed of the synchronous speed of the supply frequency. This motor is synchronous motor. We can consider a synchronous machine as a DC motor without commutator and supplied from an AC source.

Construction of Synchronous Machine

We know there must be a relative rotational motion between the rotor and the stator in order to develop a rate of change of flux in the machine. The rate of change of flux is essential to produce electrical energy and generate the voltage difference. In DC motor we have seen the field excitation is given to the stator coil while the current carrying conductor is the rotor winding or armature winding.