Mechanical Simulations Regarding the Influence of Paper Insulation Degradation on the Radial Mechanical Strength of Continuously Transposed Conductors for Power Transformers

Abstract

The short circuit withstand capability of power transformers describes the ability of the windings to withstand electromagnetic forces resulting from current density in the conductors and magnetic stray fields. Especially operationally aged transformers often have a reduced short circuit strength what can lead to irreversible deformation of windings if high fault currents occur. Short circuit strength is to some degree dependent on the mechanical strength of the conductors. Mainly the cellulosic insulation materials experience degradation during operation time due to high temperatures and moisture. Hence a reduction in short circuit strength can be correlated to some degree with the aging of the cellulose. In this paper the influence of paper insulation around Continuously Transposed Conductors (CTC) on their mechanical strength will be analyzed by a simplified analytical model as well as by a FEA based mechanical simulation model.