First power from Three Gorges1 October 2003
Power was generated for the first time from the Three Gorges Dam on the Yangtze River in southern China in July 2003, ten years after construction began in 1993.
The Three Gorges project is a major project in China's programme to develop its hydropower and reduce dependence on coal fired power stations. It has attracted international attention as the largest hydroelectric power station under construction, but for the Chinese the primary purpose of the project is flood control and water supply.
The Yangtze river (known as the Changjiang in Chinese) rises in the plateau area of southern Quinghai province in north-west China. This is part of the eastern Tibetan plateau at an elevation of between 4 000 and 5 000m. The river then flows 6 300km through southern China to the sea at Shanghai. Two thirds along its length the river passes through a series of narrow limestone and sandstone gorges which extend for nearly 200km. Near the downstream end of these gorges at the town of Sandouping the bedrock is granite and it is this site which has attracted attention over the years as a suitable location for a dam. Downstream of Sandouping the Yangtze flows in an open plain past major cities and with large industrial developments and areas of cultivated land protected by levees on either side. It is the flooding of these areas which has become an increasing problem in recent years.
Major floods causing extensive damage and loss of life occurred in 1870, 1931, 1935, 1954, 1981, 1991 and again in 1998. The scale of the problem can be appreciated by the fact that in the 1998 flood the cost of providing emergency protection for the city of Wuhan and the other downstream cities as well as protecting the areas of cultivated land together with the cost of clearing up the damage afterwards was reported to be comparable with the capital cost of the proposed dam. In addition more than 2 000 people died in the floods which affected 8 million people. Flooding also appears to have become more frequent recently because of the cutting down of trees in the upper catchment area to clear land for agriculture and possibly due to global climate change.
The flood flow in the summer of 1998 was estimated to be in excess of 60 000 cubic metres per sec and the reservoir has been designed to regulate the maximum flow downstream of the dam to about 30 000 cubic metres per sec, which can be accommodated within the present flood defence works.
Historically the maximum floods have been estimated to be in excess of 100 000 cubic metres per second and a number of smaller hydroelectric storage reservoirs being built on the upstream tributaries will help to mitigate the intensity of floods in the future.
The reservoir storage will also be a benefit in drought years. In the past the natural flow has fallen as low as 2 500 cubic metres per sec and the stored water will maintain a downstream flow of at least 5 000 cubic metres per sec which is necessary for navigation on the river and to ensure that saline intrusion from sea water at the mouth of the river does not penetrate sufficiently far upstream to damage the agricultural land.
For comparison, the average October flow of the Thames at Teddington weir in the UK is about 55 cubic metres per sec.
The second main purpose of the project is to supply water to Beijing, Zhengzhou and the other northern cities. There is a serious shortage of water in northern China for both domestic use and for agricultural irrigation, and this shortage has been exacerbated by the demand for more tourist hotels. In 1981 the thermal power stations in Beijing had to close because there was shortage of cooling water which resulted in industry losses estimated at 2 billion yuan, and in 1992 some sections of the Yellow River, which supplies much of Beijing's water, had almost dried up. It is estimated that for the northern cities alone there is a shortfall of the order of 17 million cubic metres per year which will need to be provided from the Yangtze river, and possibly twice that amount is needed for agricultural use.
The project will also improve navigation on the Yangtze river. When the reservoir is full ships will be able to navigate upstream of the dam as far as the city of Chongqing. A ship lock with a capacity for 10 000 ton barges and a ship lift for passenger ships and smaller barges of 3 000 tons has been built into the dam. The volume of traffic carried by barge is expected to increase from 10 million tons per year at present to 50 million tons, and the transport costs to decrease by one-third.
Environmental impact study
The first serious proposal to build a dam at the Three Gorges was put forward in 1919 by Dr Sun Yat-sen, the founder of modern China, but the economic and political problems arising from the Japanese war, the civil war and the communist revolution delayed the development. A feasibility study was completed in 1989, political approval was given in 1992 and construction started in 1993.
As with all modern large scale projects part of the preliminary studies for the project included a comprehensive environmental impact study which was undertaken of the whole Yangtze basin. This study demonstrated that there were positive impacts in the middle and lower reaches of the river but negative impacts in the reservoir area, and that the negative impacts could be alleviated by suitable countermeasures.
The flooded area upstream of the dam will cover 24 500 ha of agricultural land and will require about 850 000 people to be moved from their homes to higher ground. The resettlement programme has been tackled seriously by the planners and resettlement started in 1993. This is the largest single undertaking in the whole project and the costs of the resettlement programme are about 40% of the whole budget. New homes above the reservoir level have been built for 1.1 million people, but one third of those to be moved are farmers and finding new land for them to farm is more difficult than allocating land for urban housing and industry. The new land is more suitable for cash crops such as tea and citrus than the basic foods of wheat, rice and vegetables that the farmers grew at the lower levels. The government recognises it will have to import grain into the region from other parts of China to make up for the shortfall.
The area of cultivated farmland downstream of the dam which will be protected from flooding when the project is completed is 1.5 million ha, which is 60 times the area of farmland inundated upstream of the dam.
Particular care is being taken to prevent pollution of the new reservoir by the trade and domestic wastes from the adjacent cities. The city of Chongqing alone produces an estimated 1200 million tonnes of industrial wastewater and an estimated 300 million tonnes of sewage every year. At present only about a third of the industrial wastewater is treated and almost none of the sewage. The World Bank has contributed £62 million for building new sewage works and a further £156 million for treating wastewater and solid wastes. This should benefit the economy by allowing the reservoir to develop a new source of food by the introduction of fish farming and aquaculture.
Design and construction
The design of the dam is straightforward and conventional; it is the size of the project which is unusual. The main structure is a concrete gravity dam founded on granite with a maximum height of 183m. It is 2.3km long. There is a central spillway and two machine halls on the downstream toe of the dam, one on each side of the spillway. The left bank (north) power station will contain 14 x 700MW Francis turbines and in the right bank (south) power station there will be 12 x 700 MW Francis turbines. The rated head is 81m but varies from a minimum of 71m to a maximum of 113m. The total installed capacity will be 18.2 GW and the estimated annual output will be 84.7 TWh.
There is sufficient space on the south bank for a further six 700MW turbines in an underground power station which will add a further 4.2GW.
The design and construction followed closely that of the smaller Gezhouba dam completed in 1988 across the Yangtze at Yi Chang 38km downstream of the Three Gorges site. This was the first dam built across the Yangtze river and it was intended that the experience gained from designing, building and operating it would be incorporated in the design of the Three Gorges project. Gezhouba is also a gravity dam, 70 m high, with two power stations which together contain 21 Kaplan turbines with a total capacity of 2.7GW. The annual output is 15.7 TWh, but this will increase to about 20 TWh after completion of the Three Gorges dam as a result of the improved river regulation.
Of the 14 turbines and generators in the left bank power station a contract for eight generators was awarded to ABB (which later sold its power generation interests to Alstom). As a separate contract, GEC Alsthom (now Alstom), with Kvaerner Energy AS of Norway (now part of GE) as subcontractor, received the order to supply the associated turbines. The other six units were awarded to a consortium of General Electric Canada, Voith Hydro and Siemens (now Voith Siemens Hydro). An important part of both contracts is the requirement to work in partnership with Chinese companies to support local design and manufacture and to allow a substantial transfer of technology to enable Chinese companies to compete for the contract for the 12 turbine generators in the right bank power station. The Chinese partners are Harbin Electric Company for Alstom and Donfang for the GermanCanadian consortium.
The ABB-designed generators have a stator bore of 18.8m, a rated speed of 75 rpm and a rated output of 778 MVA. Large diameter slow speed generators of this size are sensitive to thermal expansion, centrifugal forces and forces involved in fault disturbances, and in their design ABB used the concept of oblique elements in the generator design to meet the requirements of roundness, concentricity and stability of the generators in all conditions.
Water cooling is provided on the stator winding, using hollow conductors made of stainless steel, and air cooling for the stator core and field winding.
The rotor mass is 2000 t and the combined thrust and guide bearing is designed for a thrust load of 5 500 t and is of the self pumping type with external coolers.
Centre of the system
During the flood season June to September the power station will provide baseload and for the rest of the year it will provide peak load when the operating conditions are expected to require the machines to stop and start twice a day.
The supply area for the Three Gorges power station within a radius of 1000 km could cover the provincial power networks of central China, east China, south China and north China, as well as the power network of Sichuan province, which lies immediately to the west of the Three Gorges power station.
Most of the output from the Three Gorges power station will initially go to Central China and east China because they have fewer power resources than south China and north China. North China has substantial coal reserves and is the thermal power base of China, and south China has abundant hydroelectric power resources. In addition some of the output from the Three Gorges power station will be allocated to Sichuan Province because although it is rich in hydroelectric resources it is comparatively undeveloped and it will be more directly affected than the other regions by the construction of the dam and the creation of the reservoir.
Of the estimated annual output of 84.7 TWh from the Three Gorges power station, 5 TWh will be allocated to Sichuan, and the rest divided between central China and east China.
Using network balancing and a power system optimisation model this indicated that the optimised power and energy to be transmitted to east China would be between 6-8 GW and 18.6-26.0 TWh, leaving approximately 10 GW to be transmitted to central China.
Electrical transmission generally in China is 500/220 kV AC. Two exemptions are the Northwest Power Network which uses 330kV AC and the Gezhouba hydroelectric power station, which is connected to Shanghai in East China by a 1.2 GW HVDC line at + 500kV. The new transmission lines from the Three Gorges power station to Sichuan province will be designed for 2 GW at 500 kV AC, and to Central China will be 12 GW at 500 kV AC.
After considering the alternatives it was decided to use DC transmission to East China and Shanghai and therefore there will be two new HVDC + 500kV lines each with a transmission capacity of 3 GW, which together with the original 1.2 GW HVDC +500 kV line will make a total capability of 7.2 GW.
DC transmission has operational advantages and avoids stability problems but is more expensive because it requires equipment which has to be imported into China. However provision will be made to manufacture some of the equipment in China with the aid of imported technology.
By 2009 when the Three Gorges Project is due to be completed the power station will contribute to the frequency and voltage regulation on the system and the maintenance of a high quality power supply, and when the provincial networks are interconnected to form a national grid then the Three Gorges power station will be at the centre of the new system.
The overall decision making body for the project is the Three Gorges Project Construction Commission which is chaired by the Premier of the State Council and whose members include local politicians. The organisation responsible for the financing, construction and management of the project is the China Yangtze Three Gorges Development Corporation located near the construction site at Yi Chang City. This corporation has several divisions including the engineering construction division which is responsible for the overall co-ordination and management of the construction. The organisation in charge of the planning research and design is the Changjiang Water Resources Commission with access to advice from panels of international specialists.
The initial civil engineering contracts were awarded by competitive bidding to more than ten Chinese contractors, and the Harza Engineering Company of the US was appointed to supervise the construction. Contracts for the first 14 turbines and generators in the left bank power station were let to Western manufacturers and it is expected the 12 turbines in the right hand power station will be built by Chinese manufacturers.
Construction started in 1993 with the building of a cofferdam to an island in the centre of the river to enclose the area of the left bank power station and the central spillway. These structures are now completed and another cofferdam has been built to enclose the area of the right bank power station while the water is being impounded behind the completed left bank power station and spillway. The right bank power station and all other outstanding work will be completed by 2009.
Project costs and funding
The original cost of the works based on 1993 prices is quoted as £6.5 billion (90.09 billion yuan). This is the sum of the project construction works estimated at £3.6 billion and the resettlement costs at £2.9 billion. These costs exclude price escalation and loan interest during the construction period. The final cost by the time the project is completed in 2009 is put at about £15 billion. Steady and reliable sources of funding are crucial factors for the success of the project, any delay in construction resulting from a lack of funds could cause huge economic losses.
The two main sources of finance for the project are funding from central government and funding from loans.
The central government funding is from three sources, the main source is a tax on the energy supplied by the power networks throughout the country. The annual energy consumption in China is in excess of 1100 TWh and the annual incremental rate of energy consumption over the next ten years is expected to be between 4% and 5%. The fund was established in 1992 and the tax was initially imposed at a rate of 0.003 to 0.007 yuan/kWh, the level of the tax in each area depending on the extent to which the local region will benefit from the scheme.
Electricity used in the poorest regions is exempt as is electricity used for agricultural irrigation and for drainage purposes. This tax contributes about half the costs of construction.
The second source of income is from the Gezhouba power station, ownership of which has been transferred to the Three Gorges Project Development Corporation (who are also owners of the TGP) and which generates 15.7 TWh per year. Part of the revenue has been allocated to the construction of the TGP. This will contribute 10 billion yuan to the project.
The third source is from the sale of electricity from the TGP itself as more machines start generating. From now until the project is completed the output is estimated to be 300 TWh and the income will contribute to the later stages of construction and to the repayment of the loans.
The major loans will be from the Chinese State Development Bank, which is providing 30 billion yuan, and also some domestic bonds. Foreign loans of about 13 billion yuan are mainly in combination with export credits for procurement of mechanical and electrical equipment, large construction machines, special materials, techniques and management.
The Three Gorges Project's economic internal rate of return is estimated to be between 14.8% and 15.6%, which exceeds the legal social discount rate in China of 12%. According to the present information the TGP's financial internal rates of return are all more than 10% in the different fund raising sources. It is estimated that all the loans can be repaid and all the investment can be recovered within 10 years after the completion of the project. The owners consider the project a financially sound and rational investment.