Applications of the 3:1 pole-changing motor

Besides the obvious application of providing two separate and economical running speeds, the application of the 3:1 pole-changing motor to obtain controlled starting, stopping and reversing of industrial drives is considered in some detail. For the latter types of drive, an investigation is made of the energy loss involved, and a comparison with other methods of control is made. It is shown that various asymmetrical connections of the primary winding for the larger pole-number can provide useful characteristics, for both squirrel-cage and slip-ring machines, and, in general, a 2-phase connection of the primary winding for the larger pole-number is likely to be more satisfactory than a 3-phase connection.