6.1 Introduction

Some devices such as the tank and accessories of a transformer, ship hulls, air-gaps in machines, contactors or magnetic recording heads, shielding, etc. are mainly made up of sheet or line type parts of thin air-gaps or cracks. Modeling these parts using traditional finite volume elements used in 3D software is tiresome, and even impossible. Moreover, the skin effect in ferromagnetic materials increases the difficulties of meshing eddy current problems in under sinusoidal conditions. To cope with these difficulties, it is possible to use special "shell elements" for the modeling of magnetic or thin conducting regions, "surface impedance" elements for the modeling of conducting regions having a low skin depth, etc. This chapter presents these special elements.

6.2 Different Special Elements and their Interest

We call a "thin region", an region which has a low thickness compared to its other dimensions, and "neighbor regions", the external regions which have a common border with the thin region.

Electrotechnical devices are also made of line type parts such as clamping beams, bus bars of transformers, windings, etc.

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Meshing thin regions and line regions using an automatic mesh generator, which generates tetrahedral elements in 3D (and triangular elements in 2D), result, because of the low thicknesses or weak sections, in a very significant number of elements or in elements which are too long. Some problems are difficult, even impossible, with current computing tools. The tetrahedral or triangular finite elements can have low accuracy when they are too long.

An alternative...