P.A.M. graded concentric windings for 2-speed single-phase induction motors

The principle of pole-amplitude modulation is described in relation to pole-changing concentric windings for single-phase motors. It is shown that satisfactory performance can be achieved at two speeds, using single `main¿ and `auxiliary¿ windings which are similar to those commonly employed in single-speed fractional-horsepower motors. Speed selection is effected by means of a simple switch, and, in some cases, only three control leads are needed. The geometrical properties of pole-changing windings are discussed, and, by way of example, windings for 6/8 poles and 10/6 poles are described in detail. Test results of a typical 6/8-pole motor are included, for four different starting and running conditions, together with the appropriate switching arrangements.