The evolution of microprocessor-based intelligent electronic devices (IEDs) equipped with Ethernet communications capabilities presents new opportunities to make substation protection and automation systems more reliable, available, stable, and cost-effective. A substation automation system (SAS) provides integration, coordination, and reliable monitoring and control for electric generation, transmission, subtransmission, distribution, and customer substations. This paper presents a modular, scalable automation system (MSAS) and discusses its components and their arrangements in detail. The proposed MSAS can be used for different distribution substations configuration and any future extension can be included with minimum change in existing design and settings.