Wavelet Transform approach for differential protection of three-phase transformers

This paper proposes a novel differential protection technique of three-phase transformers using Wavelet Transforms (WTs). The Wavelet Transform is an efficient signal processing tool used in non stationary signals with fast transition studies (high frequency components). The three phase differential currents are the input signals used on-line in the proposed formulation. The performance of the proposed formulation is evaluated through simulation of different internal faults and switching conditions on a 138 kV system containing a 25 MVA transformer (138/13,8 kV). Simulations studies are made with ATP/EMTP software. The paper also presents a study of the optional wavelet analysis selection that includes both the optimal mother wavelet and the optimal number of levels of resolution. The proposed formulation was constructed in MATLABreg environment. The case study shows that the proposed algorithm is highly accurate and effective when compared to traditional differential relay protection.