Eddy current losses

If the magnetic flux changes, a voltage is induced in the electrical conductors surrounding it. As iron is also electrically conductive, such induced voltages also arise in the iron itself. These lead to so-called eddy currents (circular currents), which heat the material.

The level of the induced voltage depends on the cross-sectional area, the magnetic flux density and the frequency. The eddy current losses increase quadratically with the induced voltage, which leads to undesirable energy losses in the form of heat.

To reduce these losses, the iron is divided into thin, electrically insulated sheets. Due to the smaller cross-sectional area of the individual sheets, less voltage is induced in each case, while at the same time the electrical resistance for the eddy currents increases.

This so-called laminating – i.e. the division into stacked and insulated sheets – significantly reduces the eddy current losses. However, this also slightly reduces the magnetic conductivity of the iron, which is taken into account in the design by the so-called iron fill factor.