Advances in Digital Protection of Power Transformer

Abstract

newline quotIn order to distinguish between internal fault and magnetizing inrush in power transformer, second harmonic component criteria have been presently utilized. However, the situations like adequate amounts of the second and fifth harmonic components during an external fault on the adjacent transmission line and advancement of low-loss amorphous core materials may lead to a malfunction or delay in operation of the conventional harmonic restraint based differential relay. Therefore, it is necessary to develop an improved technique for differential protection of the power transformer which is capable to discriminate between internal faults and other non-internal events. newlineIn the first stage of research work, a combined S-transform and Support Vector Machine based method is presented to distinguish between internal faults and other disturbances. In the second stage of research, algorithms based on superimposed and sequence components of differential currents have been presented to achieve high sensitivity during internal faults. In both the methods, Modified Discrete Fourier Transform algorithm is used to extract different positive and negative sequence components of differential currents. Based on the derived sequence components, the Internal Fault Detection Factor and Internal Fault Detection ratios is calculated for the superimposed and sequence component based method, respectively. Afterwards, a quartile based differential scheme is developed in the third stage of research work. In this method, Fault Detection Ratio (FDR) has been computed to detect internal fault from quartiles of the differential current. The threshold value of the FDR has been determined from the mathematical models of internal fault, magnetizing inrush and over-excitation conditions, and further, validated with the help of the simulation dataset obtained from different operating conditions of the power transformer. Thus, the present research works are likely to benefit significantly in the field of differential protection of power t