CORE LOSS PREDICTION COMBINING PHYSICAL MODELS WITH NUMERICAL FIELD ANALYSIS

An improved procedure for calculating iron losses in electrical machine cores is presented. It is based on physical models and experiments on losses in magnetic laminations, under one- and two-dimensional fields, and exploits a finite element computation of the flux distribution in the core. Physical modelling relies on the basic concept of loss separation, extended to the case of vectorial magnetic flux with generic elliptical loci. Starting from a theoretical formulation of power losses under unidirectional fields and generic induction waveform and its extension to the case of elliptical flux, general expressions are derived for the hysteresis, excess and classical loss components in two dimensions. Quasi-static and 50 Hz total losses under alternating sinusoidal flux and pure rotational flux are the sole experimental data needed for a complete loss prediction. In the present work, two different types of nonoriented FeSi 3.2% laminations are considered, which are assumed to be assembled into a model three-phase motor core. By means of a 2D finite element analysis, the distribution of magnetic field and induction in the core is obtained for different values of the supply current and the loss calculation is carried out. A comparison with standard loss calculation methods points to the detrimental role of two-dimensional fluxes, although this may not be fully appreciated in conventional 50 Hz induction motors.