Part symmetrisation of 3-phase windings

Polyphase symmetrisation has become a valuable technique in the design of pole-amplitude-modulated (p.a.m.) windings. Electrical unbalance in asymmetrical windings has been almost completely eliminated by its application. Difficulties have remained only in a few, but very important, special cases, such as in p.a.m. machines with very small numbers of slots per pole per phase. Part symmetrisation is an extension of the basic symmetrising principle. It permits either the negative-sequence winding component, or the zero-sequence winding component, but not both, to be eliminated from a 3-phase winding. It has found application mainly for the elimination of the negative sequence winding component, since the zero sequence has little or no adverse effect in a winding connected in star. Many p.a.m. windings with a high zero-sequence content for one or other of the main pole numbers have been designed and are currently in use. One such winding, for 4/6 poles in 24 slots, is discussed in detail.