Alstom Delivers Most Powerful Unit in the World to the Xiangjiaba plant

Alstom has successfully delivered the first generating unit at the Xiangjiaba hydropower plant in China. The 800MW Francis turbine and 889MVA generator unit passed a reliability trial run of 72 hours and recently began commercial operation.

Each generating unit has a maximum output equivalent to a small nuclear power plant and is claimed to be the most powerful ever built. When completed the station, which is owned by the China Three Gorges Corporation (CTG), will have a total capacity of 6400MW of renewable power generation.

Awarded to Alstom in autumn 2008, the Xiangjiaba contract covered the design, engineering, manufacturing and supervision of erection and commissioning of four 800MW Francis turbine/generator units. The units supplied by Alstom incorporate numerous technological breakthroughs. The turbine runner, almost 10m in diameter and weighing over 400 tonnes, has an advanced hydraulic design to ensure very smooth machine behaviour even in challenging operating zones.

In order to achieve an optimal generator design at such high power outputs, Alstom provided the world’s first air-cooled 23kV stator windings. Such windings require high quality raw materials, careful design and high dimensional precision during manufacturing. Until recently only one hydro power plant operated at such a voltage, with windings supplied by Alstom, through using water cooling through the stator windings to evacuate the heat created during electricity generation.

The challenge at Xiangjiaba was to build 23kV air-cooled stator windings, which require less auxiliary equipment, space and maintenance. In-depth research on ventilation and stator windings, including extensive testing of stator bars, was used to validate the design of the generator. The tests during commissioning and now the successful connection to the grid are the final elements which confirm this latest technological breakthrough in the design of large rotating electrical machines.

This project is one of the series of successful co-operations between Alstom and CTG, which included deliveries in Three Gorges Left Bank, Three Gorges Right Bank and Three Gorges Underground.