EMF EQUATION OF THREE PHASE SYNCHRONOUS MACHINE

EMF EQUATION


Let P= No of Poles F= Flux per pole in webers, N= speed in RPM, f= frequency in Hz


Z ph = No of conductors connected in series in phase


Tph= No of turns connected in series per phase


Kc= Coil span factor Kd= Distribution factor


Flux cut by each conductor during one revolution=PF webers


Time taken to complete one revolution= 60/N sec


Average emf induced per conductor= PF/60/N= PFN/60 volts


Averagw emf induced per phase= (PFN/60)*Zph= PFN/60x 2 Tph= 4 Ff Tph


RMS value of EMF induced per phase= average value x form factor = 4.44 FTpf f


Form factor = 1.11


Taking into consideration the coil span factor and distribution factor of the winding Actual EMF induced per phase
E ph= 4.44 Kc Kd f F Tph

Coil span factor K c
The ratio of induced emf in a coil when the winding is short pitched to the induced emf in the same coil when it is full pitched is called a coil span factor or pitch factor or chorded factor. It is generally denoted by Kc and its value is always less than unity

Distribution factor Kd
The ratio of induced emf in the coil group when the winding is distributed in number of slots to the induced emf in the coil group when the winding is concentrated in one slot is called a distribution factor or breadth factor.