Winding factor analysis of star-delta windings

Windings utilizing the star-delta (Y-D) topology are known to offer an improved MMF spectrum as the main winding factor is increased while parasitic spatial harmonics are decreased or even cancelled. Although several windings were proposed in the past, winding factors were mostly calculated individually depending on the specific winding under consideration. By applying classical theory this research presents a detailed analysis of winding factors. Closed analytical terms for Y-D winding factors are derived, covering distributed as well as fractional-slot windings. It is shown that all known Y-D windings can be described by a modified group- or zone factor. The general design procedure is presented and several design examples are discussed briefly.