From Vision to the World's Largest Dam
Of the Great Yangtze River of China flowed a great vision but Dr Sun Yat-sen, the founding father of modern China. Dr Sun saw the tremendous economic benefits of building a dam on the Yangtze as a part of his economic development plan for an underdevloped China. Dr. Sun was particularly interested in using the vast hydropower resources of the river to produce the electricity needed to build factories for making artificial fertilizer, the only means he could envision for China to make the leap in agricultural productivity needed to feed its growing population.
He also saw the area of the gorges as the most suitable spot for building a dam to generate that electricity. Dr. Sun further elaborated on this idea in 1924, in a lecture he gave on his "Third Principle of the People, Peoples' Livelihood":
Consider the tremendous water power in the Kui Gorges of the upper Yangtze. Some who have studied the stretch of river between Ichang [Yichang] and Wanshien [Wanxian] estimate that the water power there could generate over thirty million electrical horsepower. Such an immense power is much greater than that produced at present in any country. It would not only supply all the railways, electric lines, and factories in the country with power, but it could be used to manufacture staple fertilizers.
Consider again the Yellow River which at Lungmen Waterfalls could also generate many million electrical horse power. You see how great are China's natural resources! If the water power in the Yangtze and Yellow rivers could be utilized by the newest methods to generate electric power, about one hundred million horse power might be obtained. Since one horse power is equivalent to the power of eight strong men, one hundred million horse power would be equivalent to eight hundred million man power. A man works eight hours a day, according to the law in most countries; a longer working-day is injurious to the worker's health and lessens production. . . Man power can be used only eight hours a day, but mechanical horse power can be used all twenty-four hours. This means that one horse-power for a day and night accomplishes as much work as twenty-four men. If we could make use of the Yangtze and the Yellow river water power to generate a hundred million horse power, or twenty-four hundred million man power, and let this great electrical energy work for us, China would produce a great deal, and would certainly turn her poverty into riches.
In 1932, seven years after Dr. Sun's death, the Construction Committee of the Kuomintang, a party founded by Dr. Sun, which took power in 1927, organized a prospecting team to survey the hydroelectric power generation of the upper reaches of the Yangtze River. The team examined several alternative plans and recommended dams at one of two possible sites, at Huanglingmiao and at Gezhouba. The project was to include a 12.8-meter-high water-head dam with an installed generating capacity of 300 megawatts (MW), and equipped with shiplocks.
Because the nation was not peaceful, it was not until December 14th 1994, when construction began. The dam was expected to be fully operational in 2009, but due to additional projects such as the underground power plant with 6 additional generators, and due to the complexity of the ship lift, the dam is not expected to become fully operational until about 2011. The dam raised the water level the third time to 172.5 meters by the end of year 2008. The dam is entirely designed by Chinese Engineers.
The project costs 180 billion yuan, over 20 billion yuan less than the initial estimated budget of 203.9 billion yuan, just under 30 billion USD. This is because the calculation accounts for the effect of inflation, and the lower costs are attributed to a low inflation rate in recent years. Until the end of 2008, the total investment reached 148.365 billion yuan, among which, 64.613 billion yuan on construction, 68.557 billion yuan on the relocation of affected residents and 15.195 billion yuan was spent on the interests of financing. It is estimated that the cost of construction will be recovered when the dam has generated 1000 TWh of electricity, which is estimated to sell for 250 billion yuan.
The Three Gorges Dam is the world’s largest hydro-electric power station by total capacity, which will be 22,500 MW. It will have 34 generators. 32 will be main generators, each with a capacity of 700 MW, and the other 2 will be plant power generators, each with capacity of 50 MW. Among those 32 main generators, 14 of them are installed in the north side of the dam, 12 in the south side and the remaining 6 in the underground powerplant in the mountain south of the dam. After completion, the expected annual electricity generation will be over 100 TWh,18% more than the originally predicted 84.7 TWh, since 6 generators were added in 2002.
Each of the main generators weighs about 6000 tonnes and are designed to produce at least 700 MW of power. The designed head of the generator is 80.6 m. The flow rate varies between 600 m3/s to 950 m3/s depending on the head available. The Three Gorges Dam project installs Francis turbines. The diameter of the turbine is 9.7/10.4 m (VGS design/Alstom's design). It rotates at a speed of 75 rpm. The normal rated power of the generator is 778 MVA. The maximum power is 840 MVA. The power factor is 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 height of the stator is 3.1/3 m. It is the biggest stator in the world. The load at the bearing is 5050/5500 tonnes. The average efficiency of the generators is over 94%, and the highest is 96.5%. More than 8 of the 32 generators are made in China. Most of the generators are water-cooled. Some newer ones are air-cooled, which are simpler in design, manufacture and easier to maintain.
The total capacity of the plant is currently at 18.30 GW. The 14 generators in the north side of the dam have already been installed. The first one (No.2 ) started to power on July 10, 2003. The last one (No.9) started to power on September 7, 2005. All of the 14 generators first ran to full power (9800 MW) on October 18, 2006 after the water level had been raised to 156 m.
The 12 generators in the south side of the dam have already been installed. The first generator (No. 22) in the south side of the dam started working on June 11, 2007. The last generator (No. 15) on the south side of the dam was completed and brought to the power grid on Oct.30, 2008. The sixth generator in the south side (No. 17) started working on December 18, 2007. It brought the total capacity of the dam to 14.1 GW, surpassing the generating capacity of Itaipu (14.0 GW), to become the largest hydroelectric power plant in the world. The seventh generator in the south side (No. 17) started working on December 27, 2007. The eighth generator in the south side (No. 24) started working on April 25, 2008. The ninth generator in the south side (No. 19) started working on June 18, 2008. The tenth generator in the south side (No. 16) started working on July 2, 2008. The eleventh generator in the south side (No. 23) started working on August 19, 2008.
Added to the project in 2002, the underground power plant and its six generators are still under construction. As of July 1, 2009 the Three Gorges Dam Project had generated 319.9 TWh of electricity, almost one third of the 1000 TWh it needs to generate to cover the cost (see Economics). With 18,300 MW installed capacity, the generation capacity of the Three Gorges Dam Project is about 4,300 MW more than that of the Itaipu Dam. In July 2008, the Three Gorges Dam generated 10.3 TWh of electricity, the first time it has generated more than 10 TWh in a month. On June 30, 2009, after the Yangtze River flow rate increased to over 24000 m3/s, all the 26 main generators were switched on, producing 16,100 MW of power, which is less than the maximum capacity, 18,300 MW, because the head available during flood season is less than the required to reach the maximum capacity. During a flood occurred in early August, 2009, the Three Gorges Dam main generators reached their design maximum output of 1820 MW the first time for a short period of time, thanks to the elevated upstream water level and the large river flow.
During dry season from November to May next year, the Three Gorges Dam power output is limited by the Yangtze River's flow rate, as seen from the diagrams on the right. During the flood season when there is enough flow, the power output is limited by the plant generating capacity. The maximum possible power output curves were calculated based on the average flow rate at the dam site, assuming the water level is at 175 m and the plant gross efficiency is 90.15%. The actual power output in the year of 2008 was obtained based on the monthly electricity sent to the grid. The data came from the State Grid Corporation. There are several reasons why the actual power output is significantly smaller than the maximum power output. First, the dam was not operating at 175 m for the most time of the year 2008, thus the water flow though the dam has less potential energy to produce electricity. During the flood season, in order to make room for the flood, the dam lowered the water level to 145 m. Second, a few generators were being installed in 2008 thus the plant have not reached its current capacity until the end of the year. Also, the number might be slightly smaller than the total electricity generated in the table below because the diagrams on the right is based on the electricity sent to the power grid while the table is based on total electricity generated.
Power is sent in three directions. The 500 kV DC transmission line to the East China Grid has a capacity of 7,200 MW. There are three 500 kV DC transmission lines: HVDC Three Gorges-Shanghai (3,000 MW), HVDC Three Gorges-Changzhou (3,000 MW) and HVDC Gezhouba - Shanghai (1,200 MW). The 500 kV AC transmission lines to Central China Grid have a total capacity of 12,000 MW. The 500 kV DC transmission line HVDC Three Gorges-Guangdong to South China Grid has a capacity of 3,000 MW and supplies Guangdong.
In the original plan, it was expected to provide 10% of electricity consumption in China. However, China’s demand for electricity has increased at a higher rate than was planned, and if fully operational now, it would support about 3% of the total electricity consumption in China.
The Three Gorges Dam will potentially reduce the coal consumption by 31 million tonnes per year, cutting the emission of 100 million tonnes of greenhouse gas, millions of tonnes of dust, 1 million tonnes of sulfur dioxide, 370 thousand tonnes of nitric oxide, 10 thousand tonnes of carbon monoxide and a significant amount of mercury into the atmosphere. The elimination of the fossil fuel also reduces the energy consumption in mining, washing and transporting about 31 million tons of coal from northern China to the load centre in south and east China.
Since the dam started generating power on July 10, 2003, total power production is equivalent to 84 million tonnes of standard coal and reduces carbon dioxide emission by 190 million tons, sulfur dioxide by 2.29 million tonnes and nitroxides by 980,000 tonnes.
From 2004 to 2007 a total of 198 million tonnes of goods passed through the Three Gorges Dam ship locks. The freight capacity of the river increased 6 times and the cost of shipping reduced by 25%, compared to previous years, which reduces carbon dioxide emission by 630,000 tonnes. Comparing to highway transportation, the amount of fuel that Three Gorges Dam project saved between the year of 2004 and 2007 is equivalent to 4,100,000 tonnes of standard coal. Thus it reduces carbon dioxide emission by 10 million tonnes.
Since the construction of the Three Gorges Dam, many waste water treatment plants have been completed to reduce water pollution coming from the largely populated city of Chongqing and its suburban areas. According to the country's Ministry of Environmental Protection; until April 2007, there have been more than 50 waste water treatment plants installed with their total capacity reaching 1.84 million tonnes per day. More than 65% of the waste water is treated before being dumped into the Three Gorges Dam reservoir. About 32 land sites deposit were completed and could handle 7,664.5 tonnes of solid waste every day.
“The FAO’s research suggests that the Asia-Pacific region will, overall, gain about 6,000 square km of forest in 2008. That is quite a turnaround from the 13,000 square km net loss of forest each year in the 1990s. The main reason is China’s huge reforestation effort. This accelerated after terrible floods in 1998 convinced the government that it must restore tree cover, especially in the mighty Yangtze’s basin” upstream of the Three Gorges Dam.
The most significant function of the dam is to control flooding, which is a major problem for the seasonal river of the Yangtze. Millions of people are living downstream of the dam, with many large, important cities like Wuhan, Nanjing and Shanghai situated adjacent to the river. Plenty of farm land and the most important industrial area of China are built beside the river.
The reservoir's flood storage capacity is 22 km3(18 million acre feet, 1 km3 = 1 billion cubic meter). This capacity will reduce the frequency of major downstream flooding from once every 10 years to once every 100 years. With the dam, it is expected that major floods can be controlled. If a "super" flood comes, the dam is expected to minimize its effect. In 1954 the river flooded 193,000 km2 (74,518 sq mi) of land, killing 33,169 people and forcing 18,884,000 people to move. The flood covered Wuhan, a city with 8 million people, for over three months, and the Jingguang Railway was out of service for more than 100 days. In the event of a recurrence of the 1954 flood that carried 50 billion m3 of water, the Three Gorges Dam could only divert the water above Chenglingji, still leaving 30 to 40 billion m3 of flood water to be diverted. Also the dam will not protect the large tributaries such as the Xiangjiang, Zishui, Yuanshui, Lishui, Hanjiang, and Ganjiang from flooding, due to the location of the dam.
In early August 2009, the largest flood in five years passed through the dam site. The dam demonstrated its ability to control the flood by limiting the water flow to less than 40,000 cubic meter per second, thus raising the water level upstream of the dam from 145.13 meters on August 1, 2009 to 152.88 on August 8,2009. The total amount of flood water reserved was 4,270,000,000 cubic meters and the river flow was cut by 15,000 cubic meter per second at the most.
The Dam discharges its reservoir during the dry season between December and March every year. This increases the flow rate of the river downstream, and provides more fresh water for agricultural and industrial usage. It also improves the navigation conditions during dry season. The water level upstream drops from 175 m to 145 m, leaving room for the flooding season. This also increases the power output of the Gezhouba Dam downstream.
Since the filling of the reservoir in 2003, the Three Gorges Dam had supplied an extra of 11 billion cubic meter of fresh water to downsteam cities and farms during dry season, mitigated the effect of drought and improved navigation.
The installation of ship locks is intended to increase river shipping from 10 million to 100 million tonnes annually, with transportation costs cut by 30 to 37%. Shipping will become safer, since the gorges are notoriously dangerous to navigate. Each of the two ship locks is made up of 5 stages taking around 4 hours in total to transit and have a capacity of vessels of 10,000 tons. Critics argue, however, that heavy siltation will clog ports such as Chongqing within a few years based on the evidence from other dam projects.
The locks are designed to be 280 m long, 35 m wide, and 5 m deep (918 x 114 x 16.4 ft). That is 30 m longer than those on the St Lawrence Seaway, but half as deep. Before the dam was constructed, the maximum freight capacity of the river at the Three Gorges site was 18.0 million tonnes per year. From year 2004 to 2007, there were total of 198 million tonnes of freight passed through the Three Gorges Dam ship locks. The freight capacity of the river increased 6 times and the cost of shipping reduced by 25%, comparing to the previous years. The total capacity of the ship locks is expected to reach 100 million tonnes.
In addition to the canal locks, the Three Gorges Dam will be equipped with a ship lift, a kind of elevator for vessels.The ship lift is designed to be capable of lifting ships of up to 3,000 tons, having been reduced from the original plans where the ship lift was going to have the capacity to lift vessels of up to 11,500 tons displacement. The vertical distance travelled will be 113 metres, and the size of the ship lift's basin will be 120x18x3.5 meters.The ship lift, when completed, will take 30 to 40 minutes to ascend or descend, as opposed to the three to four hours for stepping through the main locks. One of the complicating factors the design has to deal with is that the water level can vary dramatically. The ship lift had to be designed to work properly even if the water levels that varied by 12 meters on the lower side, and 30 meters on the upper side.
The Three Gorges Dam is not only the largest hydroelectric power dam but the largest dam in the world.http://www.schilleri...es.html#authorshttp://en.wikipedia...._power_stationshttp://en.wikipedia....hree_Gorges_Damhttp://www.chinapage...neralfacts.htmlhttp://english.gov.c...tent_286355.htm
Edited by vinceliang, 05 September 2009 - 09:09 AM.