Feasibility Study for Enameled Round Copper Wire Compression within Slots of Electrical Machines

This paper discusses the compression of round magnet wires. The feasibility of forming operations within grooves of electrical machines after the winding process is investigated using a scientific methodology. This approach is motivated with the need for higher fill factors, comparable to the ones of hairpin technology. By using individual parallel conductors with higher number of turns, however, it is also possible to reduce frequency-dependent losses in higher drive speed ranges. In addition, the insulation layer quality for round wires is superior to the ones of profile wire due to the coating process, with the exception of extrusion insulations. This results in a better applicability of round wires for compression and higher voltage applications as well. At first, current state of technology is presented and applicable winding test procedures as well as a test setup is introduced. For experimental validation a model groove was designed and built. Possible groove design parameters are introduced and chosen according to a Design of Experiment approach (DoE). Different metrology approaches for the characterization of the insulation quality after processing and the resulting wire deformations are discussed. Significant input variables are pressing force, wire insulation thickness (measured in grades), number of turns per coil as well as wire diameter. Key output variables are the achieved fill factor improvement, the partial discharge voltage and the electrical resistance of the coil. The experimental plan, according to a full- factorial DoE, the chosen methodology and concluding results are being discussed based on main effect diagrams. In the outlook, the further investigation topics are outlined. It can be shown that the compression process of enameled round copper wires is well suited, up to a quality critical limit, for the production improvement of coils in grooves of electrical machines. The process therefore represents a promising approach to increase the fill factor, taking into account the electrical insulation properties of the winding. This first investigation can show that some electrical properties, such as partial discharge features, can even be improved in certain areas.