The 6400MW Xiangjiaba project, owned by China Three Gorges Corporation (CTG), is the last step of a cascade development on the lower mainstream of Jinsha River, of which Yibin County of Sichuan Province is on the left bank and Shuifu County of Yunnan Province is on the right bank.
When fully complete in 2015, Xiangjiaba will be the third largest hydropower project in the country, after Three Gorges and Xiluodu. As an important part of China’s Great Western Development Programme, the project is expected to drive local social and economic development. It will primarily supply power to China’s central and eastern regions, while at the same time meeting power demand in the Sichuan and Yunnan provinces.
The project is a multipurpose scheme. Aside from its main purpose of power generation, it has also been developed for flood control, navigation improvement and irrigation benefits. It will also trap sediment and act as a counter regulator to the larger Xiluodu scheme.
Key features of the Xiangjiaba dam
The main structures of the project include a dam, flood discharge facilities, sand flushing outlets, left-bank dam-toe waterway and power generation system, right-bank underground waterway and power generation system, left-bank vertical ship lift, navigation structures and irrigation intakes.
The concrete gravity dam has a crest elevation of 384m, a maximum height of 162m and a crest length of 909m. The left-bank dam-toe hydropower station is located to the left of the flood discharge structure and the right-bank underground hydropower station is located in the hill on the right bank.
CTG said that "fast construction technology" was used in building the concrete dam. During the construction, measures such as a dual position set pouring process was applied. Construction also called for the use of pioneering large-scale open caisson construction technology.
An artificial aggregates system with an extremely long conveyor belt system was utilized during construction. The aggregate system had a processing capacity of 3200 t/h and production capacity of 2600 t/h, the largest in China. Semi-finished aggregate was transported using the high capacity 31km-long belt conveyor, primarily arranged in tunnels. The conveyor, which featured changing dip angle and high belt speed, was the largest in China.
The project’s size, implementation of China’s largest ever caisson group, complex engineering, geological conditions and advanced construction technology all meant Xiangjiaba set a precedent for domestic hydropower construction.
Equipment and suppliers
The project Xiangjiaba hydro proejct includes eight turbine generator sets.
July 2013 witnessed the commissioning of the project’s underground powerhouse, containing four units manufactured by Alstom. These 800MW class units coupled with a 889 MVA generator, are the most powerful hydroelectric generating units in the world. Each unit is able to supply the yearly electricity consumption of approximately 5 million inhabitants during a year.
The four units were designed and manufactured in Alstom’s factory in Tianjin, China, and were delivered in a record time for such large machines – at an average of one unit every two months. After a first phase of reliability trials, the units began successively commercial operation between November 2012 and June 2013.
Each unit for the Xiangjiaba plant includes an 800 MW class Francis turbine coupled to an 889 MVA generator. The generators are the only air-cooled generators in the world with 23kV windings. This high voltage allows an optimised electrical design for such a high power output. At almost 10m in diameter, the turbine runners weigh over 400 tons.
Other providers of key equipment to the project include: Harbin (four turbine sets) Xi’an Electric Switch Electric Co., Ltd Xi’an Electric Group for gas insulated switchgear (GIS); Baoding Tianwei Baobian Electric for main transformers; EnergyStar for the governor system; Siemens for the excitation system; Nanjing NR Electric for the relay protection system; and Beijing IWHR Technology Co., Ltd for the computer monitoring system.
Major benefits: from power generation to CO2 reduction and flood control
The Xiangjiaba hydropower plant is the earliest operational project following the Three Gorges power station and is a major milestone in CTG’s development. After completion, the project is expected to bring a number of major benefits in terms of power generation, energy saving and emission reduction, navigation, flood control, sediment control, irrigation and cascade reverse regulation. It will also have social and economic benefits.
As a backbone power source of the West-East Power Transmission Project, the Xiangjiaba power plant brings grid connection benefits; supplies power mainly for the four provinces in China’s central region, China’s eastern region as well as Yunnan, Sichuan and Chongqing; substantially eases tight energy supply in these regions.
With an annual electricity output of 30.747TWh, Xiangjiaba is expected to replace a coal-fired power plant of equal size, resulting in an annual consumption reduction of some 14 million tons of raw coal and a corresponding CO2 emission reduction of some 25 million tons.
The Xiangjiaba hydropower project brings major flood control benefits, and its combined operation with the Xiluodu hydropower project will improve flood prevention in the downstream coastal cities of Yibin, Luzhou and Chongqing from the current 5-10-year recurrence to 50-100-year recurrence.
The project may also serve to irrigate nearly 3.75M square meters of farmland in Sichuan and Yunnan.
Xiangjiaba’s navigable structures are designed according to Class 4 channel standard and allows for passage of a 2x500t vessels. At the same time, the reservoir will inundate 84 obstruction rapids, resulting in much better shipping conditions.
When fully completed in 2015, the plant will substantially drive local economic development, help improve the local environment, ease power supply and optimise the energy mix.
Further information
An indepth article on the Xiangjiaba project, and wallchart, were published in the December 2013 issue of IWP&DC.
