Generalised approach to the analysis of asymmetrical three-phase induction motors

The growing interest in single-winding multi-speed induction motors, in which some unbalance of the windings has been in many cases inevitable, and the use of normal fractional slot windings, in which some unbalance has to be accepted, makes it an important task to devise a general method for predicting the performance of induction motors with asymmetrical stator windings. The paper presents a new original method for analysing such windings. The analysis is based on revolving-field theory and three-phase symmetrical-component theory. The analysis starts from inside the machine using the current sheet approach, taking into account the harmonics effect, and ends up with viewing the machine from outside as an electrical network having easy to calculate parameters. The analysis is supported by experimental results obtained from a test model built for this purpose.