Overall, while both distribution and transmission systems require robust protection to ensure grid stability and reliability, the specific requirements and challenges vary based on the voltage level, system complexity, and operational characteristics of each. The transmission system is the high-voltage network that carries bulk power from generation plants to substations near load centers. The aim of this technical article is to cover the most important principles of four fundamental relay protections: overcurrent, directional overcurrent, distance and differential for transmission lines, power transformers and busbars. Overcurrent Protection (OCP) 2).