Optimum designs of 1:2 pole-changing motor

A survey of current theory and practice of the 1:2 pole-changing induction motor reveals wide differences among writers and manufacturers. As a step towards resolving these, the most commonly used design and connections are re-examined with reference to their speed-torque designations, theoretically by the recently established criteria and experimentally by test on a small 2/4-pole machine. This leads to the optimisation of the electric and magnetic circuits and the eventual identification of the designs and connections that will give the smallest machines for various types of drive. The optimised ´variable-torque´ design is shown to give over 15% more output than its conventional counterpart. Interpreting the findings in terms of 4/8-pole machines, it is shown that the optimum connection for constant-torque drive and, in many cases depending on the availability of stampings of alternative bore diameters in the given frame, the optimum connection for constant-power drive are different from those usually designated for such purposes. In the process, many of the current ideas and practices are found to be unsound. The principles and methods of optimisation used are applicable to the design of pole-changing motors in general.