ALEM · ADDITIONAL LOSSES IN ELECTRICAL MACHINES

Electrical motors consume about 40 % of the electrical energy produced in the European Union. About 90 % of this energy is converted to mechanical work. However, 0.5-2.5 % of it goes to so called additional load losses whose exact origins are unknown. Our ambitious aim is to reveal the origins of these losses, build up numerical tools for modeling them and optimize electrical motors to minimize the losses.As the hypothesis of the research, we assume that the additional losses mainly result from the deterioration of the core materials during the manufacturing process of the machine. By calorimetric measurements, we have found that the core losses of electrical machines may be twice as large as comprehensive loss models predict. The electrical steel sheets are punched, welded together and shrink fit to the frame. This causes residual strains in the core sheets deteriorating their magnetic characteristics. The cutting burrs make galvanic contacts between the sheets and form paths for inter-lamination currents. Another potential source of additional losses are the circulating currents between the parallel strands of random-wound armature windings. The stochastic nature of these potential sources of additional losses puts more challenge on the research.We shall develop a physical loss model that couples the mechanical strains and electromagnetic losses in electrical steel sheets and apply the new model for comprehensive loss analysis of electrical machines. The stochastic variables related to the core losses and circulating-current losses will be discretized together with the temporal and spatial discretization of the electromechanical field variables. The numerical stochastic loss model will be used to search for such machine constructions that are insensitive to the manufacturing defects. We shall validate the new numerical loss models by electromechanical and calorimetric measurements.