Transmission line protection system for increasing power system requirements

This paper describes a protective relay for fast and reliable transmission line protection that combines elements that respond only to transient conditions with elements that respond to transient and steady state conditions. In this paper, we also present an algorithm that prevents Zone 1 distance element overreach in series-compensated line applications and show how to prevent corruption of the distance element polarization during pole-open conditions. We also introduce an efficient frequency estimation logic for single-pole-tripping (SPT) applications with line-side potentials. This logic prevents distance element misoperation during a system frequency excursion when one pole is open. We also discuss an algorithm and logic to prevent single-pole reclosing while the fault is present, avoiding additional power system damage and minimizing system disturbance. Applying these algorithms and logics results in a protective system suitable for increasing power system requirements such as heavy loading, SPT, series line compensation, and shunt line compensation.