This book discusses current and essential issues regarding: NATIONAL POWER SYSTEM, POWER SUBSTATIONS, MODELLING OF OPERATING REGIMES, METHODOLOGY FOR CALCULATING ELECTRICITY LOSSES IN POWER TRANSFORMERS, RETECHNOLOGIZATION AND OPTIMIZATION and SCADA PROGRAMME USAGE. Power substations are critical nodes in the electrical grid, acting as transition points where voltage levels are adjusted and power is distributed across regions. As energy demands rise, renewable integration grows, and infrastructure ages, the need to retechnologize and optimize these substations becomes increasingly important. Retechnologization involves upgrading or replacing outdated systems with modern, digital technologies, while optimization focuses on enhancing performance, efficiency, and reliability.