EMF Equation of DC Machines

EMF EQUATION

Let φ be the flux per pole in webers.

Let P be the number of poles.

Let Z be the total number of conductors in the armature. All the Z conductors are not connected in series. They are divided into groups and let A be the number of parallel paths into which these conductors are grouped.

So each parallel path will have Z/A conductors in series.

Let N be the speed of rotation in revolutions per minute (rpm).

Consider one conductor on the periphery of the armature. As this condition makes one complete revolution, it cuts Pφ in webers.

As the speed N is N rpm, the time taken for one revolution is 60/N secs.

Since the emf induced in the conductor = rate of change of flux cut.

Since there are Z/A conductors in series parallel path, the emf induced,

The armature conductors are generally connected in two different ways, viz. lap winding and wave winding. For lap wound armature, the number of parallel paths is equal to the number of poles (i.e., A = P). In wave wound machines, A = 2 always.