T&D World Magazine

Hydropower Plant in China Will Have Gas-Insulated High Voltage Transmission Line

Siemens Energy is constructing a high voltage gas-insulated transmission line (GIL) for China’s second largest hydropower plant "Xiluodu," currently under construction in the southwest of the country on the Jinsha Jiang river. The total tube length for this line is 12.5 km. The project involves seven three-phase systems, each with a length of approximately 600 m. For Siemens, this is the most comprehensive GIL installation to date. The gas-insulated transmission lines provide the vertical connection between the gas-insulated high voltage switchgear (GIS) in the power plant cavern at the foot of the dam and the overhead line at the edge of the dam wall. The gas-insulated high voltage transmission line is designed for a power capacity of 3900 MVA at a voltage of 550 kV and a rated current of 4500 A. The order, which was placed by China Three Gorges Project Corp., Yichang, has a value of about EUR 30 million. Commissioning of the GIL link is planned for June 2013.

In a hydropower plant such as the one at the Xiluodu dam, which has a rating of 12,600 MW, large amounts of energy need to be transferred from the foot of the dam to the overhead power transmission line at the upper end of the dam wall. Gas-insulated transmission lines are particularly well suited for this purpose thanks to their high load capacity. Using a GIL instead of a high-voltage cable has the added advantage of its special design that eliminates any risk of fire. Transmission losses from a GIL line are also lower than with conventional high-voltage cables or overhead lines. The virtually maintenance-free design enables a long service life because the gas-type insulation system effectively does not age. Moreover, the GIL tubes are welded over their entire length. This not only increases operational reliability but also gives the GIL a certain flexibility, so it can adapt to any changes in the tunnel wall that occur over time. “With our GIL technology, high power outputs can be transmitted very efficiently even in the very confined spaces that are common, for example, in this hydropower station. With this project, we are thus helping to build sustainable energy systems in China with our solutions,” stated Udo Niehage, CEO of the Power Transmission Division in the Siemens Energy Sector.

Last year, as part of the “Jinping I” dam project in China’s Sichuan province, Siemens was awarded the order to construct a similar GIL link with a total tube length of 3.2 km. Jinping I comprises three three-phase GIL systems, each with a length of 350 m, also in the form of a vertical link between the high voltage switchgear in the interior of the dam and the overhead power transmission line. Commissioning of this “pipeline for electrical power” is scheduled for mid-2012.

GIL technology is a further development of tube conductor technology. A gas-insulated extra-high-voltage line consists of an aluminum conductor tube and an aluminum enclosing tube. The GIL is suitable for connecting load centers and urban and industrial centers over a transmission length of a few kilometers, as well as for longer distances with no need to take measures for reactive power compensation. GIL lines can be routed over any terrain, including steep inclines or – as in the case of hydropower plants with dams – vertical sections. GIL technology is especially suitable for laying underground or in tunnels over short transmission lengths. Gas-insulated high voltage power lines are part of the Siemens environmental portfolio, which earned the company revenues of nearly EUR19 billion in fiscal 2008, accounting for about a quarter of Siemens’ total revenues.

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