Investigation of part winding start used in cage induction motors

The paper presents a new calculation method for induction motors with an unsymmetrical stator winding. In these cases, the usual T-equivalent circuit for stationary operation is no longer valid, but one coil of the machine has to be used as the smallest symmetry unit. Unsymmetrical windings may cause additional asynchronous and synchronous harmonic torques that might e.g. prevent the start-up. The new calculation method was verified by measurements of a large manufacturer of part winding motors where during start-up only a part of the stator winding - e.g. one of two parallel branches per phase - is connected to the mains. The calculation scheme leads to good results in the prediction of the start-up characteristic of such motors.