Providing power, decreasing emissions, preventing floods
Supplying cleaner electricity to 5 million people per year, the Xiang Jia Ba power plant is located on the right bank of the Jin Sha River, a tributary of the Yangtze. With an estimated annual power output of 30.7 billion kWh, it is one of the world’s highest output hydro turbine-generator units.
Xiang Jia Ba’s total capacity is 6,400 MW, making it China’s third largest
hydroelectric plant. In addition to power generation, the project brings flood prevention, improved shipping conditions, and agricultural irrigation to the area. And, it saves an estimated 12 million tons of CO2 emissions every year, compared to conventional fuels, which is equivalent to the emissions of 2 million vehicles.
The underground power plant uses four of GE’s 800 MW Francis turbines and 889 MVA generators, which are one of the highest capacity hydro generator units in the world. China Three Gorges Corporation, a state-owned company, leads the project and works with GE.
Innovating for Success
- At more than 10 m in diameter and weighing over 400 tons, the runner is one of
the largest in the world. It was designed by GE with a technology meant to greatly reduce hydraulic instability.
- The GE generators at Xiang Jia Ba are among the few air-cooled hydro units in the world with 23 kV windings.
- The Micadur* insulation system allows a generator-rated voltage of 23 kV and is highly resistant to oil, dust and other contaminants. Vacuum Pressure Impregnation reduces air inclusions and potential discharge and increases bar stability.
- Ventilation and cooling had to be adapted to the unit’s capacity to help keep
losses to a lower level, resulting in effective cooling, despite the long length of the stator windings.
- Such a large power air-cooled machine also needed an optimized electromagnetic design to meet customer requirements on admissible slot currents.
- Double-layer thrust bearing pads, developed and patented by GE, are used to provide unit reliability and safety by maintaining an optimum pressure distribution and, therefore, an optimum oil film thickness—despite the high axial loads of about 4,300 tons.
- The bearings in large generators are subjected to extreme pressure and temperature variations, which can cause the lubricating film to rupture, potentially severely damaging the bearings. GE developed and patented double-layer bearing pads to prevent this. In this design, a thin flexible pad plate is connected to a thick supporting plate by a field of support columns acting as springs. The columns accommodate mechanical and thermal deformations, protecting the pad. As a result of their protective qualities and durability, double-layer thrust bearing pads help to improve the levels of generator availability.