Doubly chorded fractional-slot windings

The pattern mostly used for laying out balanced fractional-slot windings is that for maximum distribution factor of the main wave. From this pattern, a large number of other balanced patterns can be obtained by a cyclic shifting of coils from one phase to the other inside the same repeatable group. The distribution factor of the main wave of these latter patterns is always smaller than that of the former pattern. The distribution factors of the harmonics are partially smaller, partially larger than those of the former pattern, so that the values of the harmonic (differential) leakage reactance of the different patterns do not differ much from each other. The advantage of the pattern with cyclic shift of coils inside the same repeatable group is that it makes possible to reduce the distribution factors of one or several undesirable electromotive force or magnetomotive force harmonics. The aim of this article is to show that the same effect of reduction of certain harmonics can be achieved by shifting of repeatable groups with respect to each other. This method of reduction of harmonics has the advantage that it is applicable to lap as well as to wave windings while the cyclic shift of coils is limited to lap windings. Further, the shift between the repeatable groups, necessary to achieve desirable results, is seen immediately, while with the cyclic shift of coils inside the same repeatable group the trial-and-error method is to be applied. On the other hand, the shifting of repeatable groups reduces the maximum possible number of parallel circuits.