7.1 Approximation of Magnetization Characteristics7.1.1 Approximation of Recalculated Characteristics7.2 Methods of Considering a Variable Magnetic Permeability7.2.1 Rosenberg’s Method for Steel Conductors (1923)7.2.2 Method of Rectangular Waves7.2.3 Neiman’s Method (1949)7.2.4 Substitute Permeability7.2.5 Computer MethodExample7.3 Dependence of Stray Losses in Solid Steel Parts of Transformers on Current and Temperature7.4 Power Losses in Steel Covers of Transformers7.5 Calculation of Stray Losses in Solid Steel Walls by Means of Fourier’s Series7.5.1 General Method7.5.1.1 Three-Dimensional Field7.5.1.2 Two-Dimensional Field7.5.2 Analytical Formulae in Case of Sinusoidal Distribution of a Field on the Steel Surface7.5.3 Computer Calculation of Power Losses in a Steel Plate Placed in the Field of Parallel BarsEXAMPLE7.6 Power Losses in a Transformer Tank7.6.1 Two-Dimensional Numerical Solution7.6.2 Three-Dimensional Analytical Calculations of a Stray Field and Losses in Tanks at Constant Permeability7.6.2.1 Field on the Tank Surface7.6.2.2 Power Losses in a Tank7.6.2.3 Influence of Flux in a Tank7.6.3 Parametric Analytical-Numerical (ANM-3D) Calculation of Stray Losses in a Tank of a TransformerExample7.6.4 Three-Dimensional Numerical Calculation of Stray Fields and Losses in Large, Three-Phase, Power Transformers7.6.4.1 FEM-3D7.6.4.2 Three-Dimensional, Equivalent Reluctance Network Method: RNM-3D7.6.5 Industrial Implementation and Verification of the RNM-3D7.6.5.1 Industrial Implementation of the RNM-3D Package7.6.5.2 Transformers without Screens, Almost Symmetric7.6.5.3 Large Transformers with an Extensive Asymmetry7.6.5.4 Influence of the Structure and Screens Configuration7.6.5.5 Screening Mistake Risk