An Ultra-High-Speed Directional Relay Based on Correlation of Incremental Quantities.

An increasing number of extra-high-voltage (EHV) and ultra-high-voltage (UHV) transmission lines have motivated the need for ultra-high-speed line protection. Traveling-wave directional protection has the advantages of ultra-high-speed operation and high sensitivity, but its reliability is doubted due to its dependence on detecting the wave-heads of traveling waves and the limitation of the limited bandwidth of the coupling capacitive voltage transformer. Incremental-quantity directional protection is another ultra-high-speed alternative. Aiming at improving the reliability of a directional relay (namely the core of a directional protection) without compromising its ultra-high-speed operation, this paper proposes a novel ultra-high-speed directional relay based on correlation of incremental quantities. The incremental voltage and current within a specific window only consist of some specific fault-generated traveling waves. Therefore, the incremental voltage is in approximately direct proportion to the incremental current. The proportional coefficient is positive or negative in the case of a reverse fault or a forward fault, respectively. The correlation coefficient of the incremental voltage and current, processed by an averaging filter, is used to identify the fault direction. Extensive simulations verified that the proposed directional relay can serve as an ultra-high-speed and reliable directional relay for non-, shunt-, or series-compensated EHV/UHV transmission lines. [ABSTRACT FROM AUTHOR]