Evaluation of Short Circuit Currents Effects on Power Transformers’ Residual Service Life

Abstract

Power transformers’ residual service life is determined by the level of their windings insulation wear. Existing regulatory documents, dedicated to the evaluation of the insulation relative wear, consider the effect of currents continuous work loads and intensive current loads on it. Short circuit currents can significantly affect the insulation of traction substations power transformers which occur rather frequently at overhead system power leads. Traction substations, that supply power to larger stations overhead systems, are affected by this influence to a greater extent. In order to more correctly evaluate short circuit currents influence the windings’ insulation wear, the statistical materials reflecting short circuit currents value and duration of the effect on power leads of the overhead system of traction substations for one of Russia's railroads within a year, were processed using an analytical method. It is suggested that wear should be divided into thermal and dynamic subjects in terms of the effect to short circuit currents using the induction method. The analysis of the results obtained proved that the windings’ insulation wear share due to short circuit current is rather significant – from 30 to 70% of overall wear. In this case, the dynamic wear accounts for larger wear percentage. It is suggested that the winding insulation dynamic wear, associated with the effect of short circuit current on the traction winding, should be taken into account for the evaluation of the residual service life of traction substations power transformers in regulatory documents based on the analysis results.