Abstract: Substations are critical components of modern power systems, enabling voltage transformation, switching, and system protection. This paper presents a comprehensive analysis of 400/220 kV substations, focusing on Air Insulated Substations (AIS) and Gas Insulated Substations (GIS). The study compares their design, operation, reliability, cost, environmental impact, and suitability for different applications. Key components such as transformers, circuit breakers, busbars, protection systems, and insulation methods are discussed in detail. The paper also highlights recent technological advancements and the future scope of hybrid substations. The analysis shows that while AIS remains cost-effective and easier to maintain, GIS offers compactness, higher reliability, and better performance in constrained environments.

Keywords: AIS, GIS, 400/220 kV Substation, Power System, Switchgear, Insulation, High Voltage Engineering

Downloads: | DOI: 10.17148/IJIREEICE.2026.14460