Relation between Electrical and Mechanical Degrees of Rotation

As stated earlier there are 180 electrical degrees between the centres of two adjacent north and south poles. Since 360 electrical degrees represents a full cycle of sinusoidal EMF, we are interested in determining how many sinusoidal cycles are generated in one complete mechanical rotation, i.e., 360 mechanical degrees for a machine having P poles. The number of electrical degrees as a function of degrees of mechanical rotation is

 where P is the number of poles (always an even integer), p is the number of pole-pairs, and θ is the number of mechanical degrees of rotation.

 Thus, a two-pole machine generates one cycle of sinusoid; a four-pole machine generates two cycles and so on, in one full revolution of the armature.