GIS-a user´s perspective

The National Grid Company plc (NGC) has more than 20 years experience of building and operating transmission voltage GIS (gas insulated switchgear) substations. NGC now has 20 major GIS substations in service or under construction on the 400 kV and 275 kV networks, together with many smaller installations operating at 132 kV, 275 kV and 400 kV. As a GIS user, NGC is looking for many features including a high level of reliability and availability, low life-cycle costs and compact substation layouts. While these requirements are clearly understood, utilities must also consider other factors that are sometimes overlooked. In this paper the author highlights three areas of potential difficulty in long-term operation of GIS which merit further consideration by both manufacturers and utilities. The three areas are: outage requirements for fault repair, pressure withstand capability of cast resin barriers, and strategic spare parts