Wide-ratio two-speed single-winding induction motors

Previous papers have described the principle of pole-amplitude modulation (p.a.m.), and its application to produce 2-speed single-winding squirrel-cage induction motors. The original theory and practice referred, specifically, to close-ratio speed changing only. This paper discusses p.a.m. on the basis of ampere-conductor distribution; and it extends its application to a considerable range of wide-ratio speed-changing induction motors. Two particular pole ratios, 4/1 and 5/1, are considered in detail, by way of example. In every case, a double-layer winding with all coils identical is used; and, in all but a very few applications, six control leads and very simple standardised control gear are required. Sample test results¿particularly of the accelerating characteristics¿are given, the machines being, in every case, fully up to normal industrial standards.