How Three Gorges Dam Powers Shanghai

Illustration for article titled How Three Gorges Dam Powers Shanghai

In case you haven't noticed, China's quickly becoming an production powerhouse. And to power these industries, China requires a massive, steady supply of power. Like the 18,300MW generated by the Three Gorges Dam's massive turbines.


The Three Gorges Dam utilizes 32 generators—thirty 700MW units and two 50MW—known as Francis turbines. Named after James B. Francis, who invented the design in 1848, these turbines are reaction-types: water loses its pressure (and energy) as it moves through the turbine and drives the runner.

As high pressure water enters through the spiral casing surrounding the guide vanes, they direct the water flow towards the runner blades (shown above). These blades spin at 75 revolutions per minute, driving a vertical shaft attached to an immense electromagnetic generator. The generator's stator—the stationary outer ring—is more than three meters tall, twenty meters wide, and is the largest of its kind.

The main array of 700MW turbines each weigh approximately 6,000 tons and pass between 21,000–34,000 cubic feet of water every second. These turbines achieve an average efficiency—how much of the water's energy is converted into mechanical energy—of nearly 95 percent.

Currently, only 29 of the 32 generators are online, the remaining turbines are undergoing testing and are expected to be operational by the end of 2012. However, even without them, the Three Gorges Dam is the largest capacity hydroelectric generator on the planet by capacity—a stunning 18,300MW. And, in the eight years, the dam has been even partially operational, it has produced over 500TWh of electricity. However, even though the dam was originally planned to produce ten percent of China's power, the country's hyper-expansion has already reduced that figure to to just three percent of 2006 numbers. And falling.

[Power-Technology - Bright Hub - Francis Turbine Wiki - Three Gorges Dam Wiki]

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I saw a documentary while this was being built (sorry, don't remember the name) that said that the silt and sediment in the water would completely foul the turbines and render the dam useless for power production in a short amount of time after it was built. Does anyone recall this or know if there is any truth to it?