The significant effects on the environment of a growing consumption of energy make essential a control of the efficiency of electric devices. It is necessary to improve the performances of these devices to have oot only a knowledge of the dissipative phenomena but also tools allowing precise simulations. Among al! these devices, the electric machines represent a very significant part. Dissipated energy is, for a great part, in electric steel sheets used for the composition of their magnetic circuit. A complete analysis of the dynamic behaviour of these sheets is carried out, it highlights its sensitivity to the induction variation speed. This analysis led, thanks to a separation of the static and dynamic aspects, to the definition of a dynamic hysteresis model which allows a precise representation of electric steel sheets. The hysteresis model is then combined with a numerical analysis method by finite elements to locally evaluate the power dissipated by the magnetic circuit of the machine. The method is validated in the case of asynchronous machines of low power. A complementary analysis, in this precise case, determine other dissipative phenomena responsible of additional losses. They originate in either the intrinsic properties of materials, like the anisotropy, or in the operations of the manufacturing process, like the short-circuits on the surface of the rotor. The taking into account of the who le of these phenomena led to a model which enable a precise prediction of electrical machines efficieocy.
