Complex R-X Diagram for Mho Relay Visualization in ATP/EMTP

Overhead transmission lines are probably the electrical component most vulnerable to lightning, short circuits, human errors, overloads and ageing due to the long trajectories they have. In this paper, the operation of the Distance Relay (21-ANSI/IEEE Standard Device Number) as primary or main protection as well as backup protection for overhead transmission lines is analyzed. The relay was modeled by using the ATP/EMTP program in order to visualize its response to different fault conditions and apparent impedance trajectories in the R-X complex diagram. MODELS programming language is used, which allows to implement algorithms that are used for structuring the functions and the operation logics of the relay. The relay behaviour under fault conditions at different locations along the line is validated by comparing it with the fault records from a real event in the electric power system of mexican utility.