The development of a new 3:1 pole-changing motor

The paper describes the development of a new 3:1 pole-changing induction motor with one 3-phase winding only, in which the performance and rating of a given machine frame for each speed are in all respects nearly equal to the best values that could be obtained from the same frame if it were wound in a normal manner for that speed only. The comparison is equally favourable both for torque ratings and for continuous horse-power ratings, and the machine is free from the crawling torques common in pole-changing motors. The number of control leads (eleven) is not unduly large, and the switch controller required is relatively simple. A simple pole-changing winding which gives a high performance for a 2 : 1 speed ratio is well known and widely used, and it seems probable that the development of a winding giving even better performance for a 3 : 1 speed ratio will find many applications, once its existence is generally known. It is believed that this is the first time a satisfactory winding of this type has been devised, although several comparable but unsatisfactory variants have previously been proposed.