Boundary Wavelet Coefficients for Real-Time Detection of Transients Induced by Faults and Power-Quality Disturbances

In the last few years, much research has been focused on wavelet coefficients for high-speed detection of transients induced by faults, high impedance faults (HIFs), and some power-quality (PQ) disturbances. However, the performance of the wavelet coefficient-based analysis in the real-time disturbance detection substantially changes with the choice of the mother wavelet, presents time delay for long mother wavelets, and may fail when the transients are overdamped, which limits the applicability of the conventional wavelet coefficients in actual digital relays. Therefore, in order to overcome all of the aforementioned drawbacks of the wavelet coefficients, this paper proposes a new wavelet decomposition process which provides additional wavelet coefficients with border distortions of a one-cycle sliding window (boundary wavelet coefficients), yielding the real-time detection of the transients scarcely affected by the choice of the mother wavelet, with no time delay for compact and long wavelets, as well as a more reliable disturbance detection than the conventional wavelet coefficients, even in cases of damped transients. In addition, a boundary wavelet coefficient requires equivalent computational burden of a conventional wavelet coefficient. The performance of the proposed boundary wavelet coefficients was assessed through the real-time analysis of records with faults, HIFs, and some PQ disturbances as well as with simulated data from transmission and distribution power systems, taking into account the effects of the fault inception angle, resistance, and distance.