Pole-changing motor using ¿-spread phase windings

A new method is described for pole changing 3-phase windings where one of the basic pole-pair numbers is a multiple of 3. Using the method, a 4/6-pole cage induction motor with a 36-slot stator winding is a standard machine at 4 poles but has a phase spread of ¿ radians at 6 poles. There is no unbalance between the phases or troublesome harmonic effects. Though the number of winding terminals to be brought out is 12, the control gear required is essentially a 3-phase double-throw switch, with two additional rows of terminals on one side. The material is supported by tests with an experimental 4/6-pole motor.