Implications of the anisotropic thermal conductivity of capacitor windings

In this paper, as a result of their laminar structure, dry BOPP windings have substantially anisotropic thermal conductivity. In the plane of the film, the thermal conductivity is about twice that of bulk polypropylene and about three times the thermal conductivity through the plane of the film. Three-dimensional finite element computations demonstrate that the anisotropic thermal conductivity of BOPP capacitor windings has a substantial effect on tolerable power dissipation within a large capacitor, as a function of how the windings are oriented within the case. For enclosure configurations that optimize heat transfer to the case, the maximum capacitor temperature can be estimated with good accuracy using analytical approximations.