AN IMPROVED ESTIMATION OF IRON LOSSES IN ROTATING ELECTRICAL MACHINES

Core losses in rotating electrical machines have been estimated through direct use of the standard Epstein loss data of the employed magnetic laminations, without introducing empirical correcting factors. The prediction is based on a numerical finite element approach to magnetic flux distribution, coupled to a physical model of losses in ferromagnetic laminations under generic flux waveform, which takes into account the specific role of the hysteresis, classical and excess loss components. An application has been made to the case of a 7.5 kW four-pole induction motor under no-load conditions. The predicted core losses turn out to be about 20% lower than the measured ones, a fact which points to an appreciable contribution of the rotor cage Joule losses and to the detrimental role played on the material properties by the residual and applied stresses introduced by lamination punching and core assemblage.