Eddy current losses

When the magnetic flux changes, an electrical voltage is induced in the electrical conductors surrounding the flux. As iron is also electrically conductive, this voltage in the iron leads to eddy currents (circular currents), which heat up the iron. 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. By dividing the iron surface into electrically insulated sheets, less voltage is induced in the individual sheet elements due to the smaller cross-sectional area and the ohmic resistance for the eddy current is greater. By dividing the iron into stacked and insulated sheets (laminating), the eddy current losses are greatly reduced. The magnetic conductivity of the iron is also reduced somewhat, which is taken into account with the iron fill factor.