Shi San Ling powers Beijing

Less than five years ago, electricity consumers in the Beijing area of China suffered frequent blackouts due to the lack of peaking capacity in the grid. Now, with the completion of the Shi San Ling pumped storage hydropower plant, reliable power supplies are ensured and power quality improved.

The recently commissioned power plant is located in Changping County, 40 km north of the urban district of Beijing. It generates 1200 GWh per annum under a maximum design head of 481 m developed between two reservoirs. Power generated from the plant is fed into the Beijing Local Grid, part of the Beijing-Tianjin-Tangshan Power System, providing a reliable peak load and emergency reserve capacity for Beijing. The plant also provides frequency regulation and reactive power modulating functions, and so plays an important role in improving the quality and operational stability of the grid.

The Shi San Ling plant was designed by the Beijing Hydroelectric Investigation and Design Institute and is owned and operated by the North China Power Group (NCPG). NCPG awarded the main construction contract for the power plant to a consortium comprising Elin Energieversorgung of Austria and the US firm Voith Hydro Inc. Financing for the project was provided by the Beijing government and the State Energy Investment Corporation. Japan's OECF provided a loan of $750 million.

The Beijing Local Grid meets the load demand of the Beijing area and also transmits power to parts of neighbouring Hebei Province. The maximum load demand in the power system is 4700 MW, with a difference of 1800 MW between peak and trough demand. Peaking capacity in the system was previously unable to meet peak demand, particularly during winter months. The NCPG therefore decided to develop a pumped storage hydropower plant using the existing Shi San Ling reservoir as the lower reservoir.

Project design

The Shi San Ling reservoir was constructed over 30 years ago, and when the Elin/Voith consortium was awarded the contract in July 1992, the upper reservoir was already under construction. Voith was the consortium leader and supplied the turbines, with Voith Heidenheim supplying the turbine-governer. Elin supplied the generators, excitation and protection systems, generator bus ducts, switchgear systems, start-up frequency converters and control systems.

The horizontal distance between the reservoirs is 2 km and they are linked by two main tunnels excavated in Mang Mountain. The upper reservoir is not naturally fed. A main and a secondary dam, with a height of 75 m and 10 m respectively, are built at the upper reservoir which has a total storage capacity of 4 450 000 m³.

From the upper reservoir, water flows to the underground powerhouse via the headrace tunnel and penstocks. The two concrete-lined headrace tunnels, of lengths 437 m and 428 m, have a maximum average flow velocity of 5.11 m/s and a diameter of 5.2 m. These pass via a double chamber surge tank into two 800 m long steel-lined penstocks. The penstocks drop 481 m and their diameter decreases from 5.2 m to 3.8 m.

The powerhouse is situated 275 m under the surface of Mang Mountain along with the transformer chamber, an access tunnel and a ventilation tunnel. It has four 200 MW Francis-type reversible pump turbines supplied by Voith and four Elin three-phase vertical shaft 222 MVA synchronous generators. Power is generated at 13.8 kV and is stepped up to 220 kV, passing through two transmission lines to the 500/220 kV Chang Ping substation 6 km away. Water exits the powerhouse passing into two 5.2 m diameter concrete-lined tailrace tunnels which lead to the lower reservoir.

In pump mode, water is pumped back up to the upper reservoir with the turbines operating in reverse mode discharging 41.7 m³/s of water. Average efficiency of the plant in reverse mode is over 91 per cent.

The static frequency converter starting is adopted in pump mode, and back-to-back starting acts as standby mode. The plant is equipped with a supervisory Bailey control system with a simplified conventional control system used as a back-up.

The first turbine-generator of the Shi San Ling plant was brought on-line in 1995. All the remaining units were then commissioned on schedule at five-month intervals. In November 1997, final commissioning of the plant was completed, less than five years after the Voith/Elin consortium signed the contract.
Tables

Main technical parameters of the Shi San Ling pumped storage hydropower plant