According to the Bertotti model, iron losses can be separated into 3 different parts: hysteresis losses, classical eddy current losses and excess losses. Flux will use this formula (for AC supply) for the power density: The Bertotti losses are detailed in the next equation:

where:

- kh is the coefficient of losses by hysteresis
- ke is the coefficient of losses in excess
- σ is the conductivity of the material
- d is the thickness of the lamination
- f is the frequency Bm is the peak value of the magnetic flux density

which becomes, within the computation frame of Flux:

kf is the coefficient of filling (the stacking factor (0 < kf < 1). This coefficient considers the electrical insulation of the laminations of the magnetic core.

To determine ke and kf, an Excel file which allows fitting the curve of the Bertotti model with the manufacturer data exists and it is provided in C:\Altair\FluxDocExamples_12.3\Tools.