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  1. ledaauto

    ledaauto Tài xế O-H

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    Hydroelectric Technology History & Development

    The first hydroelectric plant was built in the United States in 1882. This plant made use of a fast flowing river as its source. Some years later, dams were constructed to create artificial water storage areas at the most convenient locations. These dams also controlled the water flow rate to the power station turbines.
    Originally, hydroelectric power stations were small in size and were set up at waterfalls in the vicinity of towns because it was not possible at that time to transmit electrical energy over great distances. Nowadays the main reason there is large-scale use of hydroelectric power is because electrical energy can now be transmitted inexpensively over hundreds of kilometres to where it is required, making hydro power economically viable. Transmission over long distances is carried out by means of high voltage, overhead power lines called transmission lines. The electricity can be transmitted as either AC or DC.
    Unlike conventional coal-fired power stations, which take hours to start up, hydroelectric power stations can begin generating electricity very quickly. This makes them particularly useful for responding to sudden increases in demand for electricity by customers, known as “peak demand". Hydro stations need only a small staff to operate and maintain them, and as no “fuel” is needed, fuel prices are not a problem. Also, a hydroelectric power scheme uses a renewable source of energy that does not pollute the environment. However, the construction of dams to enable hydroelectric generation may cause significant environmental damage, depending on local conditions.

    Principals of Hydroelectric Power Stations

    The amount of electrical energy that can be generated from a water source depends primarily on two things: the distance the water has to fall, and how much water is flowing. Hydroelectric power stations are therefore situated where they can take advantage of the greatest fall of a large quantity of water- at the bottom of a deep and steep sided valley or gorge, or near the base of a dam (see Figure 1).

    Figure 1 Diagram of hydroelectric scheme
    (Copyright Western Power Corporation ) ​
    Water is collected and stored in the dam above the station for use when it is required. Some dams create big reservoirs to store water by raising the levels of rivers to increase their capacity. Other dams simply arrest the flow of rivers and divert the water down to the power station through pipelines.
    While a water turbine is much more sophisticated than the old water wheels, it is similar in operation (see Figure 2). In both cases, blades are attached to a shaft and when flowing water presses against the blades, the shaft rotates. The effect is the same as wind pressing against the blades of a windmill. After the water has given up its energy to the turbine, it is discharged through drainage pipes or channels called the "tailrace" of the power station for irrigation or water supply purposes or, in some parts of the world, even into the ocean.

    Figure 2 Cut-away drawing of a water turbine generator
    (Image courtesy of the Snowy Mountains Hydroelectric Scheme)
    In a conventional coal-fired (thermal) power station each "generating unit" consists of a boiler, a steam turbine, and the generator itself. A hydroelectric generating unit is simpler and consists of a water turbine to convert the energy of flowing water into mechanical energy, and an electric generator to convert mechanical energy into electrical energy. The amount of energy available from water depends on both the quantity of water available and its pressure at the turbine. The pressure is referred to as the head, and is measured as the height that the surface of the water in the dam/river is above the turbine down near the base at the outlet.
    The greater the height (or head) of the water above the turbine, the more energy each cubic metre of water can impart to spin a turbine (which in turn drives a generator). The greater the quantity of water, the greater the number and size of turbines that may be spun, and the greater the power output of the generators.

    Types of Water Turbines

    Water for a hydroelectric power station’s turbines can come from a specially constructed dam, set high up in a mountain range, or simply from a river close to ground level. As water sources vary, water turbines have been designed to suit different locations. The design used is determined largely by the head and quantity of water available at the particular site.
    The three main types are: Pelton wheels, Francis turbines, and Kaplan or propeller type turbines (named after their inventors). All can be mounted vertically or horizontally. The Kaplan or propeller type turbines can be mounted at almost any angle, but this is usually vertical or horizontal.
    The Pelton wheel (see Figure 3) is used where a small flow of water is available with a ‘large head’. It resembles the waterwheels used at water mills in the past. The Pelton wheel has small ‘buckets’ all around its rim. Water from the dam is fed through nozzles at very high speed hitting the buckets, pushing the wheel around.

    Figure 3 Pelton wheel
    (Copyright Western Power Corporation) ​
    The Francis turbine (see Figure 4) is used where a large flow and a high or medium head of water is involved.

    Figure 4 Francis water turbine
    (Copyright Western Power Corporation) ​
    The Francis turbine is also similar to a waterwheel, as it looks like a spinning wheel with fixed blades in between two rims. This wheel is called a ‘runner’. A circle of guide vanes surround the runner and control the amount of water driving it. Water is fed to the runner from all sides by these vanes causing it to spin. Propeller type turbines are designed to operate where a small head of water is involved. These turbines resemble ship’s propellers. However, with the Kaplan turbines (see Figure 5) the angle (or pitch) of the blades can be altered to suit the water flow.

    Figure 5 Kaplan and propeller type turbine
    (Copyright Western Power Corporation) ​
    The variable pitch feature permits the machine to operate efficiently over a range of heads, to allow for the seasonal variation of water levels in a dam.

    Installed Large Scale Hydroelectric Installations

    Large scale hydroelectric power systems have been installed all over the world, with the largest systems having capacities over 10, 000 megawatts (MW) (equivalent to 10 gigawatts (GW)). Each of these large scale systems require a very large dam, or series of dams, to store the enormous quantities of water required by the system. The Kariba dam in Zimbabwe, holds 160 billion m3 of water!

    Hydroelectric Installations in Australia

    The Snowy Hydro scheme is the largest in Australia, with a generation capacity of nearly 3 800 MW (see Figure 7). The Snowy Scheme consists of seven power stations (2 underground), 145km of tunnels and 16 large dams, with the largest, Lake Eucumbene, holding nine times the water volume of Sydney Harbour. Hydro Tasmania also generates a large amount of hydro power in Australia, utilising the high rainfall and mountainous terrain of Tasmania and other Australian states, and has recently been expanding further into the Pacific area. The total main transmission grid-connected generation (GWh) in the period 2003 – 04 was 212,952.83 GWh. Just over 7.2 percent of this was derived from hydro at a total of 15,399.80 GWh (ESAA, 2005). For a table of hydro installations in Australia click here.
    It is clear from the table that the vast majority of Australia’s hydro capacity is derived from the installations owned by Snowy Hydro and Hydro Tasmania, approximately 50% and 30% respectively. It is also apparent that the largest hydro projects were predominantly the first to be commissioned.

    Pumped Storage Hydroelectric Schemes

    A large number of new hydroelectric projects are of the pumped storage type. Each station reuses the water which passes through it, by storing it in catchment areas below the station and then pumping it back up to the higher catchment dams above the station in a closed circuit arrangement. This pumping is carried out in ‘off-peak’ times when there is a surplus of power available from coal, oil, or gas-fueled stations. In many countries nuclear power is used for off-peak pumping.
    When pumping is required, a reversal of roles occurs. The generator operates as an electric motor, receiving electricity from a nearby power station, and operates the turbine as a pump. The turbine receives energy instead of delivering it. However, in some pumped storage schemes there are two sets of equipment. One set is for generating and the other is for pumping. The use of pumped storage increases the total amount of power generated by the hydro power station, however, this increase is not renewable energy. The pumps are run by non-renewable sources, allowing excess electrical energy to be stored as the potential energy, as the water is raised to the height of the dam. The amount of renewable energy produced by the hydro power station remains the same.
    A number of Asian countries have major pumped storage development programs. In Korea, the Korea Midland Power Co Ltd (KOMIPO) has a 1,000 MW pumped storage power plant under construction at Yangyang. Korea Southeast Power Co Ltd (KOSEPCO) operates a 600-MW pumped storage hydro plant, and in 2004 the company finished a 800 MW pumped storage plant at Yecheon. Korea Western Power Co Ltd (KWP) operates the 600 MW Samrangjin pumped storage plant and a 600 MW pumped storage plant at Cheongsong is under construction. The Korean Southern Power Co (KOSPO) operates the Cheongpyong pumped storage plant and Korea East-West Power Co (EWP) operates the 700-MW Sanchung pumped storage plant (Platts, 2005).
    In Vietnam in 2005, the state owned power company Vietnam Electricity, published its ten year plans for three 1200 MW pumped storage plants to be built at Bac Ai, Phu Yen Dong, and Phu Yen Tay. At an estimated cost of US$2.3 billion, the three plants are designed to assist meeting the peak demand in the country. (Wilmington Media Ltd, 2005). Thailand’s 500 MW pumped storage facility in Lam Takhong, was brought on line in 2002 and is the first and largest underground powerhouse in the country, at a depth of 350 metres (EGAT, 2006).

    China boasts the Tianhuangping power station (see Figure 6). This is the largest pumped storage hydro facility in Asia and the third largest in the world, with a capacity of 1.8 GW, comprising of six 306 MW turbines. China now has 16 GW of pumped storage plants either existing, under construction, or in the planning stage (Power-Technology, 2006); (World Energy Council, 2007).

    Figure 6 The Tianhuangping Project in China is Asia’s largest pumped storage plant. (courtesy of Power Technology.com). ​

    Status of Hydro Power Worldwide

    In 1994, hydroelectric power represented 2% of the world's primary energy consumption (Ramage, 1997), and in 2004 the figure reached almost 6% (REN21, 2005). In 2004 there was around 740 GW of installed hydro capacity worldwide, generating about 2,750 TWh (2.75 x 1012 kWh) of electricity per year, and producing 16% of the world’s electricity (REN21, 2005). Hydro power supplies at least 50% of electricity production in 66 countries, and at least 90% in 24 countries. It is estimated that only 32% of the economically feasible hydro power potential worldwide has been developed so far (IJHD 1998a). In 2005 the installed hydro power capacity in Australia is 7.6 GW (DPIE, 1997). Of this capacity, 50% comes from the Snowy Hydro scheme (see Figure 7) and 30% from Hydro Tasmania.

    Figure 7 Photo of Tumut 3 Power Station, Snowy Mountains
    Copyright Snowy Hydro Limited
    In 1997, Asia had an installed hydroelectric capacity of about 100 GW (BP, 1998). Asia is the continent with the fastest growing hydroelectric industry, with many Asian countries stating that hydro power is the main focus for the development of their power sectors. China currently has the highest level of hydro power development activity in the world. The construction of the Three Gorges Dam, the world’s largest hydro power project, has been completed and partially filled to an intermediate level of power generation. The project will be fully completed in 2009 when twenty six 700 kW generators come online to generate an astonishing 18.2 GW. China has also recently completed its 1.836 GW Xiaolangdi project in 2000, one full year ahead of schedule, and is now generating 5.1 billion kWh of electricity a year, costing US$700 million dollars less than expected at $3.5 billion (see Figure 8). $1 billion of these costs were spent on resettling around 200,000 people (Power-Technology, 2006).

    Figure 8 The construction of the Xiaolangdi Project, China (courtesy of Power Technology.com). ​
    Also in China the 3.492 GW Ertan hydropower plant was constructed in a record eight years (see Figure 9). The plant boasts a 240m concrete arch dam and Asia's largest underground powerhouse (280m long by 25.5m wide and 65m high), and the world's longest diversion tunnels at 1.167km. Completed at the end of 1999, it produces around 3.9 billion kWh of power every year (Power-Technology, 2006).

    Figure 9 The Ertan Project in China has the worlds’ largest underground powerhouse (courtesy of Power Technology). ​
    In addition to China’s installed hydroelectric capacity, schemes with a total capacity of 50GW are under construction, which will double the existing capacity in the country. Construction of additional large-scale projects has commenced: Xiluodo (14.4 GW), Xiangjiaba (6 GW), Longtan (4.998 GW), Laxiwa (4.22 GW), and Xiaowan (4.2 GW). A further 80 GW of hydro power is planned, including 13 stations along the upper reaches of the Yellow River, and 10 stations along the Hongshui River (IJHD, 1998b), (International Energy Outlook, 1998).
    In other countries, Myanmar’s 280 MW Paunglaung multi-purpose hydro power station has been completed, and in the planning stages is the 140 MW Upper Paunglaung Hydel hydro power project, upstream from the larger dam. In the Philippines, the 70 MW Bakun Scheme hydro power plant was one of the first private hydro projects in the country, built by the Australian company Pacific Hydro (Pacific Hydro, 2006). Vietnam has a large number of medium to large-scale hydro schemes to be completed by 2010, including the 2.4 GW Son La scheme, which is under construction. India has 8.132 GW of hydro capacity under construction (including the 1.02 GW Tala and 60 MW Kurichu projects), with further installations planned to achieve its 50 GW installed capacity initiative. In 2006, India’s large hydro installed capacity was 29.5 GW. Indonesia’s 1 GW Cirata (see Figure 10), 112MW Kotapanjang, 210MW Musi (also a pumped storage project), and the 184 MW Sudirman hydro plants, all contribute to the total installed electricity supply to mitigate some of the pressure of the looming energy crisis in Indonesia. (IAEA, 2006).

    Figure 10 The Cirata project in West Java, Indonesia completed in 1998 has 8 x 126 MW Francis Turbines is Indonesia’s largest hydro power plant. (photo courtesy of Taisei Corp). ​
  2. winner

    winner Tài xế O-H

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    oác tiếng anh em thua :)) trình em hạn hẹp :100:

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