Investigation of AC electrical machine stators with fractional conductor windings

Abstract: Industry always searches the least expensive solution for a machine design. Therefore, there is a need for integrating different customer ordered machines within the same frame, while keeping the foundation of the mechanical design constant. Since the winding design in electrical machines is essential for the performance and relatively inexpensive to adapt, it can be used to meet different customer demands. This thesis investigates the foundations of a special winding named fractional conductor winding. An expression for winding factors for certain kinds of these windings is developed. Calculations showed that the selection of the winding distribution has effect on the air gap space harmonics produced by the winding. In some cases, the fifth and seventh space harmonics can be eliminated by the use of fractional conductor windings in combination with short pitching. The construction of a prototype fractional conductor wound induction motor was documented and is presented in this thesis. The air gap flux density in a dual slotted fractional conductor wound induction motor running at no load is studied. Analytical models are compared to results obtained by finite elements and measurements. It was found that analytical results overestimated the peak of the fundamental flux density by 13.5%. The overestimation was caused by the iron reluctance of the main flux path as well as saturation. Leakage was found to be a minor cause of this overestimation. Slot leakage and differential leakage in machines having these windings are studied. The analytical models were evaluated, with mostly good agreements, compared to finite element modeling as well as measurements.