Three Gorges Dam
The Three Gorges Dam, officially known as Yangtze River Three Gorges Water Conservancy Project is a hydroelectric gravity dam that spans the Yangtze River near Sandouping in Yiling District, Yichang, Hubei province, central China, downstream of the Three Gorges. The world's largest power station by installed capacity, the Three Gorges Dam generates 95±20 TWh of electricity per year on average, depending on the amount of precipitation in the river basin. After the monsoons of 2020, the dam produced nearly 112 TWh in a year, breaking the record of 103 TWh set by the Itaipu Dam in 2016.
The dam's body, 185 meters high and 2,309 meters wide, was completed in 2006. The power plant became fully operational in 2012, when the last of the 32 main water turbines in the underground plant began production. The last major component of the project, the ship lift, was completed in 2015.
Each of the 32 turbines, considered state-of-the-art at the time of their installation, can generate 700 MW. Combined with two 50 MW generators that power the plant itself, the Three Gorges Dam can generate some 22,500 MW—far more than the next-biggest hydroelectric plant, Brazil’s 12,600-MW Itaipu facility.
The dam improves the Yangtze River's shipping capacity and provides flood control, helping to protect millions of people from severe flooding on the Yangtze Plain. Additionally, its hydroelectric power generation has helped fuel China's economic growth. As a result, the Chinese government considers the project a source of national pride and a major social and economic success. However, it is controversial domestically and abroad. Estimates of the number of people displaced by the dam's construction range from 1.13 million to around 1.4 million. Its construction has also inundated ancient and culturally significant sites. In operation, the dam has caused some ecological changes, including an increased risk of landslides.
History
envisioned a large dam across the Yangtze River in The International Development of China. He wrote that a dam capable of generating 30 million horsepower was possible downstream of the Three Gorges. In 1932, the Nationalist government, led by Chiang Kai-shek, began preliminary work on plans in the Three Gorges. In 1939, during the Second Sino-Japanese War, Japanese military forces occupied Yichang and surveyed the area.In 1944, the United States Bureau of Reclamation's head design engineer, John L. Savage, surveyed the area and drew up a dam proposal for a "Yangtze River Project". Some 54 Chinese engineers went to the US for training. The original plans called for the dam to employ a unique method for moving ships: the ships would enter locks at the dam's lower and upper ends and then cranes would move them from each lock to the next. Groups of craft would be lifted together for efficiency. It is not known whether this solution was considered for its water-saving performance or because the engineers thought the difference in height between the river above and below the dam too great for alternative methods. No construction work was performed because of the Nationalists' worsening situation in the Chinese Civil War.
After the 1949 Communist Revolution, Mao Zedong supported the project, but began the Gezhouba Dam project nearby first, and economic problems including the Great Leap Forward and the Cultural Revolution slowed progress. After the 1954 Yangtze River Floods, in 1956, Mao wrote "Swimming", a poem about his fascination with a dam on the Yangtze River. In 1958, after the Hundred Flowers Campaign, some engineers who spoke out against the project were imprisoned.
During China's emphasis on the Four Modernizations during its early period of Reform and Opening Up, The Communist Party revived plans for the dam and proposed to start construction in 1986. It emphasized the need to develop hydroelectric power.
The Chinese People's Political Consultative Conference became a center of opposition to the proposed dam. It convened panels of experts who recommended delaying the project.
The National People's Congress approved the dam in 1992: of 2,633 delegates, 1,767 voted in favour, 177 voted against, 664 abstained, and 25 members did not vote, giving the legislation an unusually low 67.75% approval rate. Construction started on December 14, 1994. The dam was expected to be fully operational in 2009, but additional projects, such as the underground power plant with six additional generators, delayed full operation until 2012. The ship lift was completed in 2015. The dam raised the water level in the reservoir to above sea level by 2008 and to the designed maximum level of by 2010.
Composition and dimensions
Made of concrete and steel, the dam is long and above sea level at its top. The project used of concrete, used 463,000 tonnes of steel, and moved about of earth. The concrete dam wall is high above the rock basis.When the water level is at its maximum of above sea level, higher than the river level downstream, the dam reservoir is on average about in length and in width. It contains of water and has a total surface area of. On completion, the reservoir flooded a total area of of land, compared to the of reservoir created by the Itaipu Dam.
Economics
The Chinese government estimated that the Three Gorges Dam project would cost 180 billion yuan. By the end of 2008, spending had reached 148.365 billion yuan, of 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 was estimated in 2009 that the cost of construction would be fully recouped when the dam had generated of electricity, yielding 250 billion yuan; total cost recovery was thus expected to be completed ten years after the dam became fully operational. In fact, the entire cost of the Three Gorges Dam was recovered by December 20, 2013.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 from both before and after the dam had become fully operational. Additional charges were assessed as follows: every province receiving power from the Three Gorges Dam had to pay an extra ¥7.00 per MWh, and the other provinces had to pay an additional charge of ¥4.00 per MWh. No surcharge was imposed on the Tibet Autonomous Region.
Power generation and distribution
Generating capacity
Power generation is managed by China Yangtze Power, a listed subsidiary of China Three Gorges Corporation, a Central Enterprise administered by SASAC. The Three Gorges Dam is the world's largest capacity hydroelectric power station, with 34 generators: 32 main generators, each with a capacity of 700 MW, and two plant power generators, each with capacity of 50 MW, for a total of 22,500 MW. Among the 32 main generators, 14 are installed on the dam's north side, 12 on the south side, and the remaining six in the underground power plant in the mountain south of the dam. Annual electricity generation in 2018 was 101.6 TWh, which is 20 times more than the Hoover Dam.Generators
The main generators each weigh about 6,000 tonnes and are designed to produce more than 700 MW of power each. The designed hydraulic head of the generators is. The flow rate varies between depending on the head available; the greater the head, the less water needed to reach full power. Three Gorges uses Francis turbines with a diameter of 9.7/10.4 m and a rotation speed of 75 revolutions per minute. This means that in order to generate power at 50 Hz, the generator rotors have 80 poles. 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 electricity generated is then stepped up to 500 kV for transmission at 50 Hz. The generator's stator, the biggest of its kind, is 3.1/3 m in height; the outer diameter of the stator is 21.4/20.9 m, the inner diameter is 18.5/18.8 m, and the bearing load is 5,050/5,500 tonnes. Average efficiency is over 94%, with a maximum efficiency of 96.5% reached.The generators were manufactured by two joint ventures: Alstom, ABB, Kvaerner, and the Chinese company Harbin Motor; and Voith, General Electric, Siemens, and the Chinese company Oriental Motor. The technology transfer agreement was signed together with the contract. Most of the generators are water-cooled. Some of the newer ones are air-cooled, making them simpler in design and easier to manufacture and maintain.
Generator installation progress
The first north-side main generator started up on July 10, 2003. The north side became completely operational on September 7, 2005, with the implementation of generator No. 9. Full power was eventually achieved on October 18, 2006, after the water level reached 156 meters.On the south side, main generator No. 22 started up on June 11, 2007, and No. 15 became operational on October 30, 2008. The sixth began operation on December 18, 2007, raising capacity to 14.1 GW, exceeding that of Itaipu dam to become the world's largest hydro power plant by capacity.
When the last main generator finished its final test on May 23, 2012, the six underground main generators were all operational, raising the capacity to 22.5 GW. After nine years of construction, installation and testing, the power plant was fully operational by July 2012.
Output milestones
By August 16, 2011, the plant had generated 500 TWh of electricity. In July 2008 it generated 10.3 TWh of electricity, its first month over 10 TWh. On June 30, 2009, after the river flow rate increased to over 24,000 m3/s, all 28 generators were switched on, producing only 16,100 MW because the head available during flood season is insufficient. During an August 2009 flood, the plant first reached its maximum output for a short period.During the November to May dry season, power output is limited by the river's flow rate, as seen in the diagrams on the right. When there is enough flow, power output is limited by plant generating capacity. The maximum power-output curves were calculated based on the average flow rate at the dam site, assuming the water level is 175 m and the plant gross efficiency is 90.15%. The actual power output in 2008 was obtained based on the monthly electricity sent to the grid.
The Three Gorges Dam reached its design-maximum reservoir water level of for the first time on October 26, 2010, in which the intended annual power-generation capacity of 84.7 TWh was realized. It has a combined generating capacity of 22.5 gigawatts and a designed annual generation capacity of 88.2 TWh. In 2012, the dam's 32 generating units generated a record 98.1 TWh of electricity, which accounts for 14% of China's total hydro generation. Between 2012 and 2021, the dam generated an average of 97.22 TWh of electricity per year, higher than Itaipu dam's average of 89.22 TWh of electricity per year during the same period. Due to the extensive 2020 monsoon season rainfall, the annual production reached ~112 TWh that year, which broke the previous world record of annual production by Itaipu Dam equal to ~103 TWh.