This guide outlines the techniques and application considerations for determining the location of a fault on ac transmission and distribution lines. This document reviews traditional approaches and the primary measurement techniques used in modern devices: one- and two-terminal impedance-based methods, synchronized sampling methods and traveling-wave methods. Application considerations include: two-and three-terminal lines, series-compensated lines, parallel lines, untransposed lines, tapped… read more lines, underground cables, fault resistance effects, and other power system conditions, including those unique to distribution systems. read less