A.C generator

A.C power can be produced as a single phase or as a balanced poly-phase system. Though, it was found that 3-phase power generation at 50 Hz will be economical and most appropriate. Nowadays three phase generators, employed to generate 3-phase power are termed as alternators (i.e., synchronous generators). An alternator has a balanced three phase winding on the stator and termed as the armature. The three coils are so positioned in space that there axes are mutually 120° apart as shown in figure below. From the terminals of the armature, 3-phase power is attained. The rotor houses a field coil and excited by D.C. The field coil generates flux and electromagnetic poles on the rotor surface. When the rotor is driven by an external agency, the flux linkages by means of three stator coils becomes sinusoidal function of time and sinusoidal voltage is induced in them. Though, the induced voltages in the three coils will differ in phase by 120° since the current value of flux linkage with R-phase coil will occur after 120° with Y-phase coil and further 120° after, with B-phase coil. The salient pole alternator has projected poles as shown in figure (a). It has non uniform air gap and is commonly used where speed is low. On other hand the non-salient pole alternator has consistent air gap (as shown in figure (b)) and employed whenever speed is high.

                                                           Figure: 3-phase generators.