The technology of high-voltage direct current transmission (HVDC) for long-distance transportation of huge energy amounts has made its way also for grid access of offshore windfarms and interconnectors between different countries. A gas-insulated design of HVDC systems for converter and transition stations can give advantages compared to air-insulated systems.
High DC voltage ratings require large area converter stations, especially for air-insulated equipment in HVDC yards for switching and reconfiguration, such as disconnectors, earthing switches, current and voltage measuring systems, surge arresters, gas-to-air bushings and cable connections. The technology of HVDC GIS helps to decrease the footprint of converter stations of onshore and even more driven by cost saving aspects of offshore installations. Using insulating gas under pressure, space requirements of HVDC switchyards can be reduced by (70 ... 95) %.
Since both, overhead lines and underground transmission by HVDC power cables or HVDC gas- insulated lines are expected in the up-coming HVDC links and overlay networks, HVDC GIS may also be applied at transition stations between different transmission media to minimize the footprint of these stations, while integrating all relevant functionalities in gas-insulated technology. Beside the space saving aspect, the HVDC gas-insulated switchgear assemblies provide high reliability and availability, since there is no direct impact of ambient conditions like dust, salty air, ice or rain to the high-voltage parts.
From the successful tests performed so far and reference installations, it can be expected that HVDC GIS components will have equally long lifetime and minimal maintenance requirements as in HVAC GIS. The sealed and compact HVDC GIS installation would give gains both in required land area in transition stations between overhead lines and cables, and in converter stations.