For many, the world of high-voltage equipment has always been divided between air-insulated switchgear (AIS) and gas-insulated switchgear (GIS). Previously, space requirements usually predicated which option was chosen – with GIS allowing a far more compact, though more expensive, substation footprint. Stated simplistically: AIS was the preferred choice in rural areas while GIS was usually chosen in urban settings. This picture changed dramatically some 20 years ago when ABB introduced PASS.