Pole changeable three phase winding

In a pole-changeable three-phase winding for a fractional pole pair number ratio of primary p.sub.1 and secondary pole pair numbers p.sub.2 according to p.sub.1 :p.sub.2 =(3m.+-.1):3n (m, n being positive integers), with G base winding branches operative in both pole number levels, one third of which are associated with all three phases and with N null winding branches operative only at the primary pole pair number p.sub.1, the division into G base winding and N null winding branches per phase occurring according to G+N=2p.sub.1 /t, wherein t is an integral divisor of 2p.sub.1 and G is divisible by the number three, the improvement comprising a reduction in the number coils in the G base winding branches and in the N null winding branches of the individual phases predetermined increase of the winding factor and a number of additional coils disposed between the terminals for the secondary pole pair number p.sub.2 and the coil-reduced G base winding branches as additional null winding branches Z, the number of additional coils being equal to the reduction in the number of coils.