A New DC-Offset Removal Method for Distance-Relaying Application Using Intrinsic Time-Scale Decomposition

This paper presents a new adaptive method based on the intrinsic time-scale decomposition (ITD) tool for suppressing the decaying dc component effect on phasor estimation. The ITD decomposes a non-stationary fault signal into a proper rotation component (PRC) and a monotonic trend signal. The PRC is the fundamental frequency component, which is used by the discrete Fourier transform (DFT) to estimate the phasor, and the monotonic trend signal is the decaying dc component. The combination of the ITD and the DFT is a simple accurate method for phasor estimation that is applicable to protection schemes with the minimum sampling rate and also to the off-nominal power system frequency. Three types of data, i.e., mathematical, simulated, and real field fault, are examined to assess the performance of the proposed method. The obtained results confirm that the proposed method not only improves the distance relay operation, but it is not also affected by the change in the fault inception angle, fault type, fault location, power system frequency, and network topology. Furthermore, the method works both with a series compensated transmission line and a parallel transmission line.

I. Introduction

The Discrete Fourier Transform (DFT) is one of the most common techniques to estimate the phasors in modern protective relays. Since the harmonic components, the decaying dc component, and the fundamental frequency component exist in fault signals, the DFT requires the filtering process to estimate the phasor accurately. The aliasing phenomenon is minimized by using a low-pass filter. Moreover, to suppress the decaying dc component in the current signals, further filtering of the signal is an inevitable pre-processing stage [1] , [2].