The third zone protection of distance relay serves as a backup for fault on the longest transmission line which is adjacent to the line to be protected. For the accurate detection of fault, its reach setting is curtailed to 100% of the primary line plus 100% of the adjacent longest line. Such an arrangement is essential mainly for a dedicated transmission systems. But some critical power system operating conditions may develop during which the operation of the third zone protection will be challenging. Under such dependable situations, the positive sequence apparent impedance tries to penetrate into the zone characteristics and distance relay provides spurious tripping. In this study, such cases have been considered and simulated using EMTDC/PSCAD software considering the Indian Eastern Regional Grid (IERG) system.