Modeling of copper sulphide migration in paper oil insulation of transformers

Corrosion of copper due to sulphur in oil has affected the performance of transformers. The fundamental processes governing corrosion of copper due to sulphur in oil are still not well understood. In this paper, the dielectric performance of paper oil insulation under conditions of copper sulphide is discussed based on changes in capacitance, Insulation resistance and Partial discharges. Electric field analysis using FEM and PD results are employed to develop an empirical model to predict PD inception of paper oil insulation when copper sulphide is present. A simple model is also proposed to explain progressive copper sulphide migration in paper insulation. The non-linear V-I characteristics of copper sulphide is discussed to explain the breakdown of paper-oil insulation.