news / 2014-06-02
Compact grid nodes for low-loss electricity transmission
The development of compact switching points for DC transmission solves a problem caused by the grid expansion: the grid nodes and feed-in systems are becoming smaller and can thus be installed more conveniently in urban areas and on platforms for offshore wind farms.
The increased use of electricity from renewable energy sources means that the number of feed-in points remote from the load centres is growing. In order to transport large amounts of electricity, for example from wind farms in the North Sea to the major consumers in southern Germany, the grid infrastructure is being expanded. Since fewer losses occur with direct current transmission over long distances than with three-phase current, engineers are researching space-saving DC solutions that can be laid underground. A particular problem of the transmission concerns the necessary switching points at grid nodes. “High-voltage direct current transmission provides the best way for achieving the low-loss transmission of large amounts of electricity and for stabilising the grids. Until now, however, there has been a lack of compact switchgear technology,” reports Denis Imamovic, Siemens’ development manager for compact systems for high-voltage direct current transmission applications.
Gas-insulated switchgear up to 320 kV is ready for the market
Until recently, space-saving gas insulation has not been available for DC transmission – only space-consuming air insulation. A research project led by Siemens has now managed to design such components. “The gas insulation enables us to achieve space savings of up to 95 per cent,” says Imamovic, whereby the direct current places other demands on the insulation than alternating current. The engineers are relying here on so-called RIP technology (Resin Impregnated Paper), which enables optimised field control in smaller system geometries.
Since all live parts are fully encapsulated, the system modules can also be installed outdoors, which means that the space required for a protective building is no longer required. The “space requirement” criterion is especially important for converter stations located in urban centres and on the collection platforms for offshore wind farms at sea. Switchgear for the voltage level up to 320 kilovolts has already been developed to market maturity. Based on long-term tests that are currently being carried out at the Technische Universität München, the researchers expect a lifespan of up to 50 years.
The engineers are now further developing the systems for the 500-kilovolt voltage level. The presented joint project on compact systems for high-voltage direct current transmission applications (abbreviated to DCCoS) is being funded by the German Federal Ministry for Economic Affairs and Energy.