Laminated steel eddy-current loss versus frequency computed using finite elements

Eddy-current loss in laminated steel cores is computed with unusual planar eddy finite elements over the wide frequency range produced in AC motor drives. The loss computed by the finite element method at low frequencies is shown to agree within 1% with a common simple formula. A formula used by radio-frequency engineers is shown to agree within 1% with the finite-element results at very high frequencies. The loss calculations are also compared with published curves from a steel manufacturer. At medium frequencies, no simple formula exists and, thus, the core loss computed by finite elements should be useful in the design of chokes and motors of AC variable-frequency drives.