Preliminary investigations on the insulating liquid used in some loading resistances to quantify premature damage causes

The aim of this paper is to report the preliminary results on the investigations performed to determine the origins and causes of heavy damages occurred under service on some static inverter module resistances. The obtained results indicate that the values of the electric and dielectric characteristics of the cooling liquid are still very good. Only the dissipation factor values show a severe increase, which is however not a limiting factor for the application in the static inverters. From the preliminary investigations, it seemed that the failure origins are due to a free burning arc between two resistance lamellas. Furthermore, some recommendations were suggested for the investigations follow up.