Eddy current loss in laminated steel cores is computed with unusual planar eddy finite elements over the wide frequency range produced in AC 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. At medium frequencies no simple formula exists, but the loss computed by finite elements is shown to agree reasonably well with some of the published data on steel laminations typically used in the cores of chokes and motors of AC drives.
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