kjernetap

kjernetap, or core loss, is the energy dissipated as heat in the magnetic core of electrical machines such as transformers, inductors and electric motors when driven by an alternating magnetic field. It is separate from winding copper loss and mechanical losses, and it limits overall device efficiency, especially at higher frequencies and flux densities.

Core losses consist mainly of hysteresis loss and eddy current loss. Hysteresis loss results from irreversible changes in the magnetic domain structure as the material's magnetization reverses with each cycle. It increases with frequency and with the peak flux density, and is often modeled as proportional to f times Bmax^α, with α around 1.6 depending on material.

Eddy current loss arises from currents induced in the conductive core by the changing magnetic flux. It scales with the square of frequency and flux, and is strongly reduced by using laminated cores, high-resistivity materials, and thin laminations or amorphous or ferrite materials.

Material choice and construction—lamination thickness, grain orientation for steel, or amorphous metals—significantly affect kjernetap. Core loss is a key consideration in transformer and motor efficiency and is specified in performance standards and datasheets.