State of the art in insulation of gas insulated substations: main issues, achievements, and trends

Nowadays power delivery grids face many challenges, among which are (1) steady growth of urban and suburban areas and the consequent reduction of space available for power facilities, (2) quest for higher power quality and availability, and (3) growing concerns about the visual impact and the electromagnetic compatibility of high voltage systems. During the last few decades, these challenges have driven R&D efforts in the field of electrical substations toward more compact, reliable, and environmentally compatible facilities. Gas insulated substations (GIS) fit these needs, although at high investment cost, mainly because of the performances of their insulation. GIS and gas insulated transmission lines (GITL or GIL) consist basically of a conductor supported by solid insulators inside an enclosure, which is filled with sulfur hexafluoride (SF6) gas [1], [2] (see Figure 1). The excellent dielectric properties of SF6 [3] make GIS much more reliable than conventional air insulated substations [4]; they also consume much less power and take up much less space. GIS components have a modular design, are filled with the minimum amount of SF6, are preassembled and tested in a controlled environment in the factory, have acceptable lifecycle costs, and can be used for indoor and outdoor applications. Other noteworthy features include an expected service lifetime in excess of 50 years, motor-operated self-lubricating mechanisms, corrosion resistance, and low fault probability [4], [5]. Recently, emphasis has been placed on partial discharge (PD) measurement techniques in GIS [6], and on the use of GIS in high voltage (HV) DC systems [7], [8].