Inverse Time Overcurrent Relaying Decision for Protection of Three Phase Transmission Line

The transmission lines are an indispensable part of the electrical power system and have a large impact on the quality of life in our communities. They transport electricity from power plants to homes and businesses. They are the backbone of modern society, providing power for everything from lights to refrigerators to electric cars. They are an essential part of the nation’s infrastructure, and when they are functioning properly, they help to keep our country moving forward. But like any complex system, transmission lines are not without fault. They can experience a variety of faults such as line to line faults, line to ground faults, double line to ground faults and three phase symmetrical faults. These faults can cause a variety of problems for the electrical system, from power outages to safety hazards. To protect transmission lines from these faults, different type of overcurrent relays are used which are normally located at substations. When a fault occurs on transmission line, the overcurrent relays are activated and the transmission line is shut down. The overcurrent relays are also used to notify the transmission line operator of faults so that the transmission line can be protected as early as possible. This paper presents the modelling and simulation of inverse type overcurrent relays using MATLAB/SIMULINK. A relaying decision is obtained based on the simulation results to determine the suitable overcurrent characteristics for the different types of faults.