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There is a necessity of circuit breaker replacement with Gas circuit breaker is to meet the day by day growing load demand, to reduce the down time to upgrade the system with current technology and to provide better protection to the substation power equipment's. To improve the efficiency and reliability and to provide the best quality of power and service to the end customer. Electromechanical relays will lag in functionalities and operations in compression with the current technology numerical relays. Numerical relays are more flexible in configuring the relay settings, having better reliability, multifunctional capability, multiple relay setting characteristics , digital communication capabilities. Numerical relays are modular based so it can be easily serviced/ replaced, Numerical relays have very less burden, having better sensitivity/selectivity, High speed operation (set/ reset), comprises auto resetting and self diagnostics features. Consumes very less space in comparison with electromechanical relays. In this paper the procedure for Gas circuit breaker and numerical relay replacement is illustrated with the substation reference drawing. I. INTRODUCTION ROTECTIVE relays play a vital role in the operation of the electrical power system. Protective relays are designed to take action when abnormal conditions occur such as short circuits, overload condition and loss of system synchronism. Protection schemes have typically been made up of discrete components such as over current relays, distance relays, auxiliary relays, and reclosing relays. All of the devices must be wired together to have a complete, functional scheme, which means time and money in the design, development, and installation process. Due to the number of components that make up these protection schemes, detailed installation tests, and routine maintenance programs can be performed to ensure that the schemes are functioning correctly. This requires a significant investment in time, money, and manpower. Increased growth in power systems both in size and complexity has brought about the need for fast, accurate and reliable protective schemes-to protect major equipment and to maintain system stability.