New 2-speed induction motors

A new method of pole changing of 3-phase machine windings is described. A standard (60°-spread, full-pitched) winding for P1 poles is used. Pole change is effected by redistributing the coils among the phases without reversing any part. On change to P2 poles, the winding has an effective spread of 120°, is exactly balanced and has a good m.m.f. waveform. Krebs´s 12-terminal delta-delta connection is used. The controller is a simple 6-phase double-throw switch. Test results of experimental 6/4, 8/6 and 8/4 pole cage induction motors are given. Windings suitable for constant-torque and constant-power drives give higher outputs than comparable versions of existing 2-speed windings.