Distance protection for multi-terminal transmission lines

In order to supply small communities or facilities in sparsely populated, remote rural areas, tapped transmission lines provide an attractive solution to provide connections at minimum cost. Using a tapped line saves the cost of building a substation at the connection point and the cost associated with the need to break the line. However, introducing a tap in the line greatly complicates the protection. The situation is further complicated by the increased use of distributed generation which may be connected to the system load side. This paper presents a protection scheme designed for protecting multi-terminal transmission lines using distance relays. The advantage of the proposed scheme is that it nearly eliminates the need for communication channels among the different protection system components. The proposed scheme has been verified by a realistic system case study. The case study is an excerpt of the Egyptian 66kV grid. The SIMULINK simulation results have proved the validity and soundness of the proposed concept.