A Model of Pole-Mounted Distribution Transformer for Lightning Failure Analysis

Abstract

As installation of lightning protection devices on pole-mounted distribution transformers has been progressing, the number of lightning failure of the transformers has been decreasing. However, some lightning failure of the transformers has occurred even though lightning protection devices have been installed. Specifically, the number of lightning failure in the primary bushings has been decreasing, but lightning failure in the primary windings has still occurred. Several transformer models have been proposed for electromagnetic transient studies. However, these models cannot calculate lightning overvoltages which generate in the transformer windings. In this paper, first, we explain differences in lightning failure aspects of the transformers by dismantling investigation. Then, we present experimental results of lightning overvoltages which generate in the primary windings. Finally, based on the lightning failure aspects of the transformers and the experimental results, we propose a transformer model which can calculate lightning overvoltages in the transformer windings, and show validity of this model by comparisons between experimental and calculated results.