SYNCHRONOUS MACHINE

Synchronous Machines are the rotating machines whose speed is determined by the "supply frequency" and "number of poles". 

Synchronous Machine rotates at constant speed known as synchronous speed.

Alternating emf in the armature coil can be generated by two ways:

(i) By rotating armature coil in uniform magnetic field with stationary field poles, or 

(ii) By keeping the armature conductors stationary and rotating the field poles.

Thus as long as there is a relative motion between the armature conductors and field, there will be a voltage generated in the armature conductors. In both the cases, waveform is a sine curve.

Majority of Synchronous Machine are having rotating field and stationary armature. It has several advantages over it.

ADVANTAGES OF ROTATING FIELD

1. Stationary Armature can be easily insulated for higher voltages.

2. Since the armature windings are stationary, they are not subjected to vibrations and centrifugal forces.

3. Output Current can be easily taken as terminals are fixed on the stationary armature. No need of using slip rings and brushes.

4. Only 2 slip rings are required for providing direct current to the rotating field, while at least 3 slip rings would be required for the rotating armature ( that too of higher voltages).

5. Size of the machine is reduced.

6. Rotating field is comparatively light and can be constructed for high speed rotations.

7. Cooling becomes more easier in the case of stationary armature.

Functionally, Synchronous Machine are of two types - Synchronous Motor and Synchronous Generator (Alternator). 

SYNCHRONOUS SPEED

Synchronous Speed is given by :

N = (120 * f) / P

where,  N = Synchronous Speed.

            f = Supply Frequency.

            P = Number of Poles.

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