Lumped magnetic circuit provides possibility for fast transient simulation of magnetic component together with power electronics circuit. The simplified geometry representation however is not able to completely reflect the real field distribution, especially when material nonlinearity is included. To model electrical characteristic of the magnetic components closer to the reality, special treatment is needed to determine geometrical parameters of the lumped representation. In this paper, modeling of the curved areas (e.g. core corners) based on permeances is presented and compared with FEM simulations.