Development of two indices based on discrete wavelet transform for transformer differential protection

Abstract

SUMMARYThis paper proposes an algorithm for transformer differential protection. The paper presents the development of two indices based on discrete wavelet transform to discriminate between internal faults and inrush currents. Each of the proposed indices, that is, the retained energy and the number of zeros can be used individually for the suggested algorithm. The proposed technique consists of decomposition of differential current signals up to a specific level and compression by level thresholding. Various simulations and analysis have been performed to determine the best compression ratio to distinguish between transformer inrush and fault currents. The performance of these indices is demonstrated by simulation of different faults and switching conditions on a modeled power system. Obtained results show that the proposed scheme is robust and reliable. Copyright © 2011 John Wiley & Sons, Ltd.