Chapter 5 examines one of the key elements of the smart grids of the future – the “digital substation” (DS). It provides a general description of DS, their structure, and principles of transformation into intelligent elements of the electric power systems of the future. A distinctive feature of a digital substation is its advanced structure, which is based on intelligent high-voltage equipment and a unified information platform. Among the most important high-voltage components are electronic transformers, which offer significant advantages over traditional electromagnetic devices. The control architecture of a digital substation comprises three typical levels: station level, bay level, and process level. In this configuration, copper wire connections between the process level and bay level can be replaced with fibre optic cables, enabling the transition from analogue signals to their digitized versions. The overall tasks of data collection and access are implemented using an integrated information platform. Additionally, the digital substation concept incorporates state-of-the-art principles for equipment condition monitoring and protection.