The enclosure has two fundamental functions: maintaining internal gas pressure and ensuring gas - tightness to prevent the release of SF6 into the atmosphere. Sheet steel materials are well - suited for fulfilling these functions. In contrast, cast steel has porosity issues and cannot guarantee the high - level gas - tightness required for Gas - Insulated Switchgear (GIS).
Steel is relatively easy to weld and shape. Steel enclosures are typically fabricated by mechanically forming steel sheets into cylinders and then welding them.
Aluminum is used for conductors in the form of extruded pipes or through casting technology. For enclosures, aluminum can be used in casting technology or with welded sheet materials, employing either longitudinal welding or spiral welding processes.
Extruded pipes are suitable for use as conductors in straight bus bar sections. However, when conductors are installed inside disconnecting or ground switches, the necessary shape and design call for casting technology.
In the past, a drawback of cast aluminum was its porosity, which led to the leakage of insulation gas into the atmosphere.
Today, most GIS enclosures are made of cast aluminum, as it offers superior performance for GIS. The attached image shows a straight conductor graphic manufactured from aluminum.
