Siemens has launched what it describes as the "first compact gas-insulated switchgear (GIS) for high-voltage direct current applications."

Describing the technology in a presentation to the recent Cigre conference in Paris, Siemens says its new 320 kV gas-insulated switchgear uses up to 95% less space compared to previous air-insulated equipment. When used in an offshore HVDC converter platform for offshore wind, "the platform size can thus be decreased by approximately 10%", the company says.

The DC direct current switchgear typically used in offshore converter stations uses air-insulated switchgear and thus requires a large amount of space because of air’s relatively low insulating capabilities. The air-insulated DC switchgear that has been used on Siemens’ converter platforms until now occupies about 4000 cubic meters. The company’s new compact GIS switchgear needs only 200 cubic meters, for the same capacity. It believes the technology will establish itself as the standard for offshore converter platforms and thereby play a major role in decreasing costs for HVDC transmission grid connections.

While gas-insulated, three-phase current switchgear is well established there has not been a corresponding gas-insulated technology for direct current applications to date. Since controlling an electric field under direct current is very complex, says Siemens, "it had not been possible until now to build gas-insulated, compact DC switchgear for HVDC transmission applications." The development of a new isolator, which can permanently withstand the demands of high-voltage direct currents, made it possible to develop the first DC GIS switchgear.

A pilot station based on 320 kV DC components that simulates the connection of an offshore wind farm to the grid is currently being operated in a long term test run, Siemens says.