The dam body was completed in 2006. Except for a ship lift, the originally planned components of the project were completed on October 30, 2008, when the 26th generator in the shore plant began commercial operation. Each generator has a capacity of 700 MW. Six additional generators in the underground power plant are not expected to become fully operational until 2011. Coupling the dam's thirty-two main generators with two smaller generators (50 MW each) to power the plant itself, the total electric generating capacity of the dam will eventually reach 22.5 GW.
The project produces electricity, increases the river's shipping capacity, and reduces the potential for floods downstream by providing flood storage space. From completion through September 2009 the dam has generated 348.4 TWh (1,254 PJ) of electricity, covering more than one third of its cost.
The Chinese state regards the project as a historic engineering, social and economic success, with the design of state-of-the-art large turbines, and a move toward limiting greenhouse gas emissions. However, the dam flooded archaeological and cultural sites and displaced some 1.3 million people, and is causing significant ecological changes, including an increased risk of landslides. The dam has been a controversial topic both in China and abroad.
The dam is made of concrete and is 2,335 m (7,661 ft) long, and 185 metres (607 ft) high. The project used 200,000 cubic metres (300,000 cu yd) of concrete, 463,000 tonnes of steel, enough to build 63 Eiffel Towers, and moved about 102,600,000 cubic metres (134,200,000 cu yd) of earth.
When the water level is at its maximum of 175 metres (574 ft) over sea level (110 metres (361 ft) above the river level downstream), the dam reservoir is about 660 kilometres (410 mi) in length and 1.12 kilometres (0.70 mi) in width on average, and contains 39.3 km3 (31,900,000 acre·ft) of water. The total surface area of the reservoir is 1,045 km².
When finished, the project is expected to have cost 180 billion yuan, 12% under budget, approximately 30 billion USD. The lower costs are attributed to a low inflation rate rather than lower spending. By the end of 2008, spending had reached 148.365 billion yuan, among which 64.613 billion yuan was spent on construction, 68.557 billion yuan on relocating affected residents, and 15.195 billion yuan on financing. It is estimated that the construction cost will be recovered when the dam has generated 1,000 TWh of electricity, yielding 250 billion yuan. Full cost recovery is expected to occur ten years after the dam starts full operation.
Funding sources include the Three Gorges Dam Construction Fund, profits from the Gezhouba Dam, loans from the China Development Bank, loans from domestic and foreign commercial banks, corporate bonds, and revenue before and after the dam is fully operational. Additional charges were assessed as follows: Every province receiving power from the Three Gorges Dam has to pay ¥7.00 per MWh extra. Other provinces had to pay an additional charge of ¥4.00 per MWh. Tibet pays no surcharge.
Power generation is managed by China Yangtze Power a listed subsidiary of China Three Gorges Corporation (CTGPC) a Central Enterprise SOE administered by SASAC. The Three Gorges Dam is the world’s largest hydroelectric power station by total capacity, eventually reaching 22,500 MW.It will have 32 generators: 30 main generators, each with a capacity of 700 MW, and two plant power generators, each with capacity of 50 MW. Among those 32 main generators, 14 are installed in the north side of the dam, 12 in the south side, and the remaining six in the underground power plant in the mountain south of the dam. The expected annual electricity generation will be over 100 TWh, 18% more than the originally predicted 84.7 TWh, resulting from the six generators added in 2002.
The main generators weigh about 6,000 tonnes each and are designed to produce more than 700 MW of power. The designed head of the generator is 80.6 meters (264 ft). The flow rate varies between 600–950 cubic metres per second (21,000–34,000 cu ft/s) depending on the head available. The greater the head, the less water needed to reach full power. Three Gorges uses Francis turbines. Turbine diameter is 9.7/10.4 m (VGS design/Alstom's design) and rotation speed is 75 revolutions per minute. Rated power is 778 MVA, with a maximum of 840 MVA and a power factor of 0.9. The generator produces electrical power at 20 kV. The outer diameter of the generator stator is 21.4/20.9 m. The inner diameter is 18.5/18.8 m. The stator, the biggest of its kind, is 3.1/3 m in height. Bearing load is 5050/5500 tonnes. Average efficiency is over 94%, and reaches 96.5%.
The State Grid Corporation and China Southern Power Grid paid a flat rate of ¥250 per MWh ($35.7 US) until July 2, 2008. Since then, the price has varied by province, from ¥228.7-401.8 per MWh. Higher-paying customers receive priority, such as the city of Shanghai.[47] Nine provinces and two cities consume power from the dam.[48]
Power distribution and transmission infrastructure cost about 34.387 billion Yuan. Construction completed in December 2007, one year ahead of schedule.[49]
Power is distributed over multiple 500 kilovolt (kV) transmission lines. Three Direct current (DC) lines to the East China Grid carry 7,200 MW: Three Gorges-Shanghai (3,000 MW), HVDC Three Gorges-Changzhou (3,000 MW), and HVDC Gezhouba - Shanghai (1,200 MW). The alternating current (AC) lines to the Central China Grid have a total capacity of 12,000 MW. The DC transmission line HVDC Three Gorges-Guangdong to the South China Grid has a capacity of 3,000 MW .
The dam was expected to provide 10% of China's power. However, demand has increased more quickly than planned. Even fully operational, it would support only about 3% of 2006 requirements.
According to the National Development and Reform Commission of China, 366 grams of coal would produce 1 kWh of electricity during 2006.[52] At full power, Three Gorges reduces coal consumption by 31 million tonnes per year, avoiding 100 million tonnes of greenhouse gas emissions,[53] millions of tonnes of dust, one million tonnes of sulfur dioxide, 370,000 tonnes of nitric oxide, 10,000 tonnes of carbon monoxide, and a significant amount of mercury.[54] Hydropower saves the energy needed to mine, wash, and transport the coal from northern China.
From 2003 to 2007, power production equaled that of 84 million tonnes of standard coal, reducing carbon dioxide by 190 million tons, sulfur dioxide by 2.29 million tonnes, and nitrogen oxides by 980,000 tonnes.
The dam increased the Yangtze's barge capacity sixfold, reducing carbon dioxide emission by 630,000 tonnes. From 2004 to 2007 a total of 198 million tonnes of goods passed through the ship locks. Compared to using trucking, barges reduced carbon dioxide emission by ten million tonnes and lowered costs 25%.
Two hazards are uniquely identified with the dam. One is that sedimentation projections are not agreed upon, and the other is that the dam sits on a seismic fault. At current levels, 80% of the land in the area is experiencing erosion, depositing about 40 million tons of sediment into the Yangtze annually.
The absence of silt downstream has two effects:
* Some hydrologists expect downstream riverbanks to become more vulnerable to flooding.
* The city of Shanghai, more than 1,000 miles (1,609 km) away, rests on a massive sedimentary plain. The "arriving silt—so long as it does arrive—strengthens the bed on which Shanghai is built... the less the tonnage of arriving sediment the more vulnerable is this biggest of Chinese cities to inundation..." Benthic sediment buildup causes biological damage and reduces aquatic biodiversity.
As of June 2008, China relocated 1.24 million residents, ending with Gaoyang in Hubei Province), about 1.5% of the province's 60.3 million and Chongqing City's 31.44 million population. About 140,000 residents were relocated to other provinces.
Relocation was completed on July 22, 2008. Chongqing City will encourage an additional four million people to move away from the dam to the Chongqing metropolitan area by the year 2020.
Allegedly, funds for relocating 13,000 farmers around Gaoyang disappeared after being sent to the local government, leaving residents without compensation.
source : wikipedia.org
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