Modelling of Oil-Paper Insulation Layers in the Frequency Domain with Cole-Cole-Functions

The measurement of oil-paper insulation systems in the frequency domain provides novel diagnostic methods for quality control of materials and high- voltage power transformers. The first task is to measure and to analyse the dielectric behaviour of oil-paper insulation systems and their dependency on material quality, moisture content and ageing products in oil, paper and pressboard. Furthermore, the geometrical layout of power transformers and the type of modelling are very important for the diagnostic. Every medium has its own special complex capacitance C_Medium in frequency domain that can be simulated with a Cole-Cole function with conductivity. The behaviour of the power transformer can be calculated from the parallel connexion and the series connexion of the individual microscopic capacitances C_Medium. The quantitative usage of the insulation layer model requires small parasitics on the boundaries, homogeneous materials of the individual layers and a uniform field. The paper describes the models of oil, paper and press- board with different values of parameters like temperature and moisture. This is the basic model for the power transformer. It describes a method of generating the different power transformer models with parameters like temperature, moisture etc. and a technique to control and show the error of measurement.