A flexible protection scheme for multi-terminal transmission lines

In order to supply small communities or facilities in sparsely populated, remote rural areas, tapped transmission lines provides an attractive solution to the challenge to provide connections at minimum cost. Using a tapped line saves the costs of building a sub-station at the point of connection together with those associated with the need to break the line. Unfortunately however, introducing a tap in the line greatly complicates the protection. The situation is further complicated by the increasing use of distributed generation which can be connected to the system. This paper introduces a novel protection scheme designed for protecting multi-terminal transmission lines. It also has the ability to be extended if and when new taps are added to the circuit. This scheme is based on a conventional carrier assisted, distance relay protection scheme and is designed to accommodate variations in tap position.