Siemens Energy is constructing a gas-insulated high-voltage line (GIL) with a total tube length of 3.2 km (2 miles) for the Chinese hydropower plant Jinping I in the Liangshan Yi district of Sichuan province.

Siemens is installing three 3-phase GIL systems, each with a length of 350 m (1148 ft), as a link between the machine transformers in the power plant cavern and the high-voltage switchgear for connecting to the overhead line. The 305-m (1000-ft) dam wall of the power plant is the highest structure of its kind in the world. As a result, the GIL has to bridge vertical sections about 200 m (656 ft) long, which necessitated special design. The high-voltage transmission system can transmit 3500 MVA of power at a voltage of 550 kV.

Ertan Hydropower Development Co. Ltd. (Chengdu, China) placed the order with Siemens. The GIL is scheduled to go into operation in mid-2012.

In hydropower plants, large amounts of energy have to be transmitted from the machine transformer inside the dam wall to the high-voltage switchgear on the surface. Due to their high performance, gas-insulated transmission lines are particularly well suited for this. Furthermore, they pose no fire risk in the power plant tunnel. The GIL systems for the Jinping I hydropower plant are designed for power capacities of up to 3500 MVA and currents up to 4000 A.

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. No measures are required for reactive power compensation, and transmission losses from a GIL line are lower than for cables or overhead lines.

GIL lines can be routed over any terrain, including steep inclines or vertical sections, and GIL technology is especially suitable for laying underground or in tunnels over short transmission lengths.