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Numerical relays offer increased functionality at lower cost, high reliability and long service life. These numerical relays play a significant role in the automation, protection and control of transmission lines in a substation. SCADA system for medium voltage substation includes a user interface called Human Machine Interface (HMI) and a number of remote numerical relays. This paper presents the development of Supervision, Control, Monitoring and Protection functions for a medium voltage substation using SCADA system with MODBUS communication. The uniqueness of the developed low cost system is the incorporation/integration of features of Remote Terminal Units (RTUs) and Intelligent Electronic Devices (IEDs) into numerical relays which improved the existing SCADA system, and the main functions of computer based control and monitoring centre. This paper also covers the detailed features such as single line diagram screen, configuration page, relay setting page, event and fault records incorporated in the design of the above SCADA system. Authors experience in commissioning of this indigenous development at medium voltage substation is also discussed. The system performance has been monitored successfully for the past few years. The relay parameters, such as real-time metering, remote circuit breaker operation and other contact status are also recorded at regular intervals and reported in the paper.