Loop selective direction measurement for distance protection

Distance relays achieve selective tripping by measuring all short circuit fault conditions within a settable reach. The direction of the fault (forward or reverse) is commonly determined with a dedicated measurement to ensure selectivity under all conditions. For the directional decision (measurement) a number of alternatives are available. This paper describes a loop selective direction measurement and illustrates by means of a typical fault why this is superior to a nonloop directional measurement such as those based on negative sequence quantities.