An Empirical Fourier Transform-Based Power Transformer Differential Protection

This paper presents a novel approach for the power transformer differential protection based on empirical Fourier transform (EFT). The EFT is a novel transform technique, which is derived from discrete Fourier transform (DFT) with certain modifications based on the nature of current waveforms during internal fault, inrush, and current-transformer (CT) saturation. The fundamental component estimated by EFT is equal to DFT estimation for internal fault currents and zero or a very low value for inrush currents and CT saturation currents. The fundamental component estimated by EFT is used in the biased restraint characteristic with a deviation factor (DF) to make tripping decisions for relays. The DF describes the waveform deviation rate of differential current waveform from a pure sinusoidal waveform. The proposed EFT-based differential protection algorithm (EFT-DPA) is validated and compared with the conventional DFT-based differential protection algorithm (DFT-DPA) through modeling for an existing real-time power transformer in Tamil Nadu Transmission Corp. Ltd. (TANTRANSCO), Tamilnadu, India. Also, the performance of the EFT-DPA is investigated with the fault recorder data taken from the field differential relay of the same power transformer. The power transformer modeling is carried using PSCAD and the EFT-DPA is implemented in MATLAB.