Enhancing Reliability of Distance Protection in Power Transmission Lines Operating Out of Step

Abstract

This study focuses on enhancing the reliability of distance protection in power transmission lines under out-of-step conditions. Wide-range fluctuations in currents and voltages cause nuisance tripping of protective relaying and automated control systems. For example, simultaneous voltage drops and current surges can cause distance protection measuring elements to miscalculate the fault distance. This error often leads to the false tripping of healthy grid components and triggering of cascading outages. We examine the distance protection starting elements that utilize positive- and negative-sequence current measurements. Currents under out-of-step conditions typically have two frequency components. This feature underlies the proposed general structure of the measuring element that selectively suppresses both frequencies. The performance of this measuring element is investigated across various individual component frequencies under out-of-step conditions. The findings reveal the uncertainty ranges for the tripping of protection measuring elements during fault events. The study also proposes methods for calculating the sensitivity of distance protection measuring elements to transmission line faults.