Eddy Current Loss in Ferromagnetic Plates of Finite Thickness, Subjected to Two Boundary Conditions of Magnetic Field at the Surface Created by Alternating Magnetizing Field/Flux

The paper presents normalized eddy current loss curve for ferromagnetic plates of finite thickness, giving variation of normalized loss, denoted as (loss factor)L with plate relative thickness, d/δ_L where d represents plate half thickness and δ_L signifies depth of penetration used under limiting nonlinear theory.

Graphical solution approach, ignoring the effect of harmonics of field quantities has been used to solve Maxwell’s field equation for thin iron plates subjected to sinusoidal magnetizing force at the surface, commonly denoted as SHS condition. Step function B₁-H approximate has been used for the magnetic characteristic of the plate material; and the result of graphical solution represented in the form of normalized eddy current loss and power factor curves. The appended eddy current loss curve has been shown useful for predicting eddy current loss in thin iron plates of varied electrical and magnetic properties, subjected to SHS condition. The result of the predicted values of eddy current loss have been compared with the corresponding test results for core losses and the two results are shown to be in close agreement within engineering accuracy for plates with relative plate thickness ≥ 0.40.

The application of the normalized eddy current loss has been attempted for predicting eddy current loss in thin iron plates subjected to the other boundary condition of the magnetic field at the surface, that is, sinusoidal current density at the surface, denoted as SJS condition and the results obtained have been compared with the corresponding test results for core losses. Surprisingly it has been found that the two results agree with each other within ± 14 percent for much thinner plates with relative plate thickness ≥ 0.28.

As such, the core losses in thin as well as thick iron plates subjected to two boundary conditions of magnetic field at the surface, namely, SHS and SJS can be assessed in the design office from the normalized eddy current loss which embodies frequency, resistivity, surface magnetizing force, Hs, saturation flux-density, Bs and plate half thickness. The power factor curve, appended can be utilized for calculating the power factor of the exciting winding circuit reflected by the magnetic circuit.