ANALYSIS OF VOLTAGE DISTRIBUTION IN POWER TRANSFORMER WINDINGS DURING VERY FAST TRANSIENT OVER-VOLTAGES

Abstract

In this work, the non-linear voltage distribution in transformer winding is in- vestigated that occurs due to switching and lightning. The major factors that contribute to premature insulation failure are lightning/line surges, switching over voltages and internal over voltages. It is imperative to determine the voltage be- havior across winding during such transient switching voltages. So requirement is to develop a suitable model which can describe accurately the voltage distribution. Various model has been proposed to determine the driving point impedance and voltage characters. As the frequency varies the model requirement also changes at low frequencies lumped or general model can be followed but as frequencies goes higher the model has to be distributed where the complete capacitive, inductive and resistive e ect of each small section need to take into consideration. In this report rst three models have been discussed. First ladder type model, then multi conductor transmission line model and then combination of both, hybrid model is discussed and di erentiated. However relevant study describes MTL model which gives highly precise results when the frequencies reach up to various MHz ranges. In the present work, rst winding parameters are calculated which is based on the geometrical structure of the winding, then work is done on the multi conductor transmission line model with the help of which voltage distribution in the winding is estimated. the modeling of the winding is done in the frequency domain.Also in the thesis work, the comparison between the continuous and interleaved wind- ing is performed, various parameter for interleaved winding is also calculated and then voltage distribution is estimated.Comparison of voltage pattern across both winding is carried out at di erent frequency. Once the model accuracy is checked it can be applied to estimate the partial discharge or any insulation failure of the winding during transients.