Q. Show Elementary Synchronous Machines?

The polyphase synchronous machine operates with direct current supplied to the field winding (assumed to be on the rotor, which is usually the case) through two slip rings and with polyphase alternating current supplied to the armature (assumed to be on the stator). The rotormmf, which is obtained froma dc source, is stationarywith respect to the rotor structure.When carrying balanced polyphase currents, the armature winding produces a magnetic field in the air gap rotating at synchronous speed, as determined by the system frequency and the number of poles in the machine. But the field produced by the dc rotor winding revolves with the rotor. To produce a steady unidirectional torque, the rotating fields of stator and rotor must be traveling at the same speed. Therefore, the rotor must turn precisely at the synchronous speed.

The polyphase synchronous machine is one in which the rotor rotates in synchronism with and in the same direction as the rotating mmf wave produced by the stator. Thus for synchronous machineswith polyphase statorwinding, the following equation relatingmechanical and electrical angular speeds is satisfied:

or alternatively, the steady-state speed at which the machine operates is known as the synchronous speed, given by

where f is the frequency of the system of which the machine is a part and P is the number of poles of the machine.