Presentation on theme: "Green Power Generation Lecture 5 Hydroelectric Power 1."— Presentation transcript:
Green Power Generation Lecture 5 Hydroelectric Power 1
2 Hydroelectricity is the term referring to electricity generated by hydropower; the production of electrical power through the use of the gravitational force of falling or flowing water It is the most widely used form of renewable energy Once a hydroelectric complex is constructed, the project produces no direct waste, and has a considerably lower output level of the greenhouse gas carbon dioxide (CO 2 ) than fossil fuel powered energy plants Worldwide, an installed capacity of 777 GWe supplied 2998 TWh of hydroelectricity in 2006GWe This was approximately 20% of the world's electricity, and accounted for about 88% of electricity from renewable sources
3 History Hydropower has been used since ancient times to grind flour and perform other tasks. In the mid-1770s, French engineer Bernard Forest de Belidor published Architecture Hydraulique which described vertical- and horizontal-axis hydraulic machines By the late 19th century, the electrical generator was developed and could now be coupled with hydraulics The growing demand for the Industrial Revolution would drive development as well In 1878 the world's first hydroelectric power scheme was developed at Cragside in Northumberland, England by William George Armstrong It was used to power a single light bulb in his art gallery. The old Schoelkopf Power Station No. 1 near Niagara Falls in the U.S. side began to produce electricity in 1881 The first Edison hydroelectric power plant, the Vulcan Street Plant, began operating September 30, 1882, in Appleton, Wisconsin, with an output of about 12.5 kilowatts By 1886 there were 45 hydroelectric power plants in the U.S. and Canada. By 1889 there were 200 in the U.S. alone
4 At the beginning of the 20th century, many small hydroelectric power plants were being constructed by commercial companies in mountains near metropolitan areas Grenoble, France held the International Exhibition of Hydropower and Tourism with over one million visitors By 1920 as 40% of the power produced in the United States was hydroelectric, the Federal Power Act was enacted into law The Act created the Federal Power Commission to regulate hydroelectric power plants on federal land and water As the power plants became larger, their associated dams developed additional purposes to include flood control, irrigation and navigation Federal funding became necessary for large-scale development and federally owned corporations, such as the Tennessee Valley Authority (1933) and the Bonneville Power Administration (1937) were created Additionally, the Bureau of Reclamation which had began a series of western U.S. irrigation projects in the early 20th century was now constructing large hydroelectric projects such as the 1928 Hoover Dam
5 The U.S. Army Corps of Engineers was also involved in hydroelectric development, completing the Bonneville Dam in 1937 and being recognized by the Flood Control Act of 1936 as the premier federal flood control agency Hydroelectric power plants continued to become larger throughout the 20th century Hydropower was referred to as white coal for its power and plenty Hoover Dam's initial 1,345 MW power plant was the world's largest hydroelectric power plant in 1936; it was eclipsed by the 6809 MW Grand Coulee Dam in 1942 The Itaipu Dam opened in 1984 in South America as the largest, producing 14,000 MW but was surpassed in 2008 by the Three Gorges Dam in China at 22,500 MW Hydroelectricity would eventually supply some countries, including Norway, Democratic Republic of the Congo, Paraguay and Brazil, with over 85% of their electricity The United States currently has over 2,000 hydroelectric power plants which supply 49% of its renewable electricity
6 Cross section of a conventional hydroelectric dam
8 Conventional (dams) Most hydroelectric power comes from the potential energy of dammed water driving a water turbine and generator The power extracted from the water depends on the volume and on the difference in height between the source and the water's outflow This height difference is called the head The amount of potential energy in water is proportional to the head A large pipe (the "penstock") delivers water to the turbine
9 Pumped-storage This method produces electricity to supply high peak demands by moving water between reservoirs at different elevations At times of low electrical demand, excess generation capacity is used to pump water into the higher reservoir When there is higher demand, water is released back into the lower reservoir through a turbine Pumped-storage schemes currently provide the most commercially important means of large-scale grid energy storage and improve the daily capacity factor of the generation system
10 Run-of-the-river Run-of-the-river hydroelectric stations are those with small or no reservoir capacity, so that the water coming from upstream must be used for generation at that moment, or must be allowed to bypass the dam.
11 Tide A tidal power plant makes use of the daily rise and fall of ocean water due to tides; such sources are highly predictable, and if conditions permit construction of reservoirs, can also be dispatchable to generate power during high demand periods Less common types of hydro schemes use water's kinetic energy or undammed sources such as undershot waterwheels.
12 Underground An underground power station makes use of a large natural height difference between two waterways, such as a waterfall or mountain lake An underground tunnel is constructed to take water from the high reservoir to the generating hall built in an underground cavern near the lowest point of the water tunnel and a horizontal tailrace taking water away to the lower outlet waterway
13 Sizes and capacities of hydroelectric facilities The Three Gorges Dam in China is the largest operating hydroelectric power station, at 22,500 MW
14 Although no official definition exists for the capacity range of large hydroelectric power stations, facilities from over a few hundred megawatts to more than 10 GW are generally considered large hydroelectric facilities Currently, only three facilities over 10 GW (10,000 MW) are in operation worldwide; Three Gorges Dam at 22.5 GW, Itaipu Dam in South America at 14 GW, and Guri Dam in Venezuela at 10.2 GW Large-scale hydroelectric power stations are more commonly seen as the largest power producing facilities in the world, with some hydroelectric facilities capable of generating more than double the installed capacities of the current largest nuclear power stations While many hydroelectric projects supply public electricity networks, some are created to serve specific industrial enterprises
15 Dedicated hydroelectric projects are often built to provide the substantial amounts of electricity needed for aluminum electrolytic plants, for example. the Grand Coulee Dam switched to support Alcoa aluminium in Bellingham, Washington, United States for American World War II airplanes before it was allowed to provide irrigation and power to citizens (in addition to aluminum power) after the war In Suriname, the Brokopondo Reservoir was constructed to provide electricity for the Alcoa aluminium industry New Zealand's Manapouri Power Station was constructed to supply electricity to the aluminum smelter at Tiwai Point.
16 The construction of these large hydroelectric facilities, and their changes on the environment, are also often on grand scales, creating as much damage to the environment as at helps it by being a renewable resource Many specialized organizations, such as the International Hydropower Association, look into these matters on a global scale.
17 Small Small hydro is the development of hydroelectric power on a scale serving a small community or industrial plant The definition of a small hydro project varies but a generating capacity of up to 10 megawatts (MW) is generally accepted as the upper limit of what can be termed small hydro This may be stretched to 25 MW and 30 MW in Canada and the United States Small-scale hydroelectricity production grew by 28% during 2008 from 2005, raising the total world small- hydro capacity to 85 GW Over 70% of this was in China (65 GW), followed by Japan (3.5 GW), the United States (3 GW), and India (2 GW)
18 Small hydro plants may be connected to conventional electrical distribution networks as a source of low-cost renewable energy Alternatively, small hydro projects may be built in isolated areas that would be uneconomic to serve from a network, or in areas where there is no national electrical distribution network Since small hydro projects usually have minimal reservoirs and civil construction work, they are seen as having a relatively low environmental impact compared to large hydro This decreased environmental impact depends strongly on the balance between stream flow and power production.
19 Micro Micro hydro is a term used for hydroelectric power installations that typically produce up to 100 KW of power These installations can provide power to an isolated home or small community, or are sometimes connected to electric power networks There are many of these installations around the world, particularly in developing nations as they can provide an economical source of energy without purchase of fuel Micro hydro systems complement photovoltaic solar energy systems because in many areas, water flow, and thus available hydro power, is highest in the winter when solar energy is at a minimum.
21 Pico Pico hydro is a term used for hydroelectric power generation of under 5 KW It is useful in small, remote communities that require only a small amount of electricity For example, to power one or two fluorescent light bulbs and a TV or radio for a few homes Even smaller turbines of 200-300W may power a single home in a developing country with a drop of only 1 m (3 ft) Pico-hydro setups typically are run-of-the-river, meaning that dams are not used, but rather pipes divert some of the flow, drop this down a gradient, and through the turbine before returning it to the stream
22 Pico hydroelectricity in Mondulkiri, Cambodia
23 Calculating the amount of available power A simple formula for approximating electric power production at a hydroelectric plant is: P = ρhrgk, where P is Power in watts, ρ is the density of water (~1000 kg/m 3 ), h is height in meters, r is flow rate in cubic meters per second, g is acceleration due to gravity of 9.8 m/s 2, k is a coefficient of efficiency ranging from 0 to 1. Efficiency is often higher (that is, closer to 1) with larger and more modern turbines Annual electric energy production depends on the available water supply. In some installations the water flow rate can vary by a factor of 10:1 over the course of a year.
24 Advantages and disadvantages of hydroelectricity Advantages Economics The major advantage of hydroelectricity is elimination of the cost of fuel The cost of operating a hydroelectric plant is nearly immune to increases in the cost of fossil fuels such as oil, natural gas or coal, and no imports are needed Hydroelectric plants have long economic lives, with some plants still in service after 50–100 years Operating labor cost is also usually low, as plants are automated and have few personnel on site during normal operation.
25 CO2 emissions Since hydroelectric dams do not burn fossil fuels, they do not directly produce carbon dioxide While some carbon dioxide is produced during manufacture and construction of the project, this is a tiny fraction of the operating emissions of equivalent fossil-fuel electricity generation Hydroelectricity produces the least amount of greenhouse gases and externality of any energy source Coming in second place was wind, third was nuclear energy, and fourth was solar photovoltaic The extremely positive greenhouse gas impact of hydroelectricity is found especially in temperate climates The above study was for local energy in Europe; presumably similar conditions prevail in North America and Northern Asia, which all see a regular, natural freeze/thaw cycle (with associated seasonal plant decay and regrowth).
26 Other uses of the reservoir Reservoirs created by hydroelectric schemes often provide facilities for water sports, and become tourist attractions themselves In some countries, aquaculture in reservoirs is common Multi-use dams installed for irrigation support agriculture with a relatively constant water supply Large hydro dams can control floods, which would otherwise affect people living downstream of the project
27 Disadvantages Ecosystem damage and loss of land
28 Large reservoirs required for the operation of hydroelectric power stations result in submersion of extensive areas upstream of the dams, destroying biologically rich and productive lowland and riverine valley forests, marshland and grasslands The loss of land is often exacerbated by the fact that reservoirs cause habitat fragmentation of surrounding areas Hydroelectric projects can be disruptive to surrounding aquatic ecosystems both upstream and downstream of the plant site For instance, studies have shown that dams along the Atlantic and Pacific coasts of North America have reduced salmon populations by preventing access to spawning grounds upstream, even though most dams in salmon habitat have fish ladders installed.
29 Salmon spawn are also harmed on their migration to sea when they must pass through turbines This has led to some areas transporting smolt downstream by barge during parts of the year In some cases dams, such as the Marmot Dam in Oregon, have been demolished due to the high impact on fish. Turbine and power-plant designs that are easier on aquatic life are an active area of research Mitigation measures such as fish ladders may be required at new projects or as a condition of re- licensing of existing projects
30 Generation of hydroelectric power changes the downstream river environment Water exiting a turbine usually contains very little suspended sediment, which can lead to scouring of river beds and loss of riverbanks Since turbine gates are often opened intermittently, rapid or even daily fluctuations in river flow are observed For example, in the Grand Canyon, the daily cyclic flow variation caused by Glen Canyon Dam was found to be contributing to erosion of sand bars Dissolved oxygen content of the water may change from pre-construction conditions.
31 Depending on the location, water exiting from turbines is typically much warmer than the pre-dam water, which can change aquatic faunal populations, including endangered species, and prevent natural freezing processes from occurring Some hydroelectric projects also use canals to divert a river at a shallower gradient to increase the head of the scheme In some cases, the entire river may be diverted leaving a dry riverbed Examples include the Tekapo and Pukaki Rivers in New Zealand
32 Siltation When water flows it has the ability to transport particles heavier than itself downstream This has a negative effect on dams and subsequently their power stations, particularly those on rivers or within catchment areas with high siltation Siltation can fill a reservoir and reduce its capacity to control floods along with causing additional horizontal pressure on the upstream portion of the dam Eventually, some reservoirs can become completely full of sediment and useless or over-top during a flood and fail
33 Flow shortage Changes in the amount of river flow will correlate with the amount of energy produced by a dam Lower river flows because of drought, climate change or upstream dams and diversions will reduce the amount of live storage in a reservoir therefore reducing the amount of water that can be used for hydroelectricity The result of diminished river flow can be power shortages in areas that depend heavily on hydroelectric power The risk of flow shortage may increase as a result of climate change Studies from the Colorado River in the United States suggest that modest climate changes, such as an increase in temperature in 2 degree Celsius resulting in a 10% decline in precipitation, might reduce river run-o ﬀ by up to 40% Brazil in particular is vulnerable due to its heaving reliance on hydroelectricity, as increasing temperatures, lower water ﬂow and alterations in the rainfall regime, could reduce total energy production by 7% annually by the end of the century
34 The Hoover Dam in the United States is a large conventional dammed-hydro facility, with an installed capacity of 2,080 MW
35 Methane emissions (from reservoirs) Lower positive impacts are found in the tropical regions, as it has been noted that the reservoirs of power plants in tropical regions may produce substantial amounts of methane This is due to plant material in flooded areas decaying in an anaerobic environment, and forming methane, a potent greenhouse gas
36 According to the World Commission on Dams report, where the reservoir is large compared to the generating capacity (less than 100 watts per square metre of surface area) and no clearing of the forests in the area was undertaken prior to impoundment of the reservoir, greenhouse gas emissions from the reservoir may be higher than those of a conventional oil-fired thermal generation plant Although these emissions represent carbon already in the biosphere, not fossil deposits that had been sequestered from the carbon cycle, there is a greater amount of methane due to anaerobic decay, causing greater damage than would otherwise have occurred had the forest decayed naturally.
37 In boreal reservoirs of Canada and Northern Europe, however, greenhouse gas emissions are typically only 2% to 8% of any kind of conventional fossil-fuel thermal generation A new class of underwater logging operation that targets drowned forests can mitigate the effect of forest decay In 2007, International Rivers accused hydropower firms of cheating with fake carbon credits under the Clean Development Mechanism, for hydropower projects already finished or under construction at the moment they applied to join the CDM. These carbon credits – of hydropower projects under the CDM in developing countries – can be sold to companies and governments in rich countries, in order to comply with the Kyoto protocol
38 Relocation Another disadvantage of hydroelectric dams is the need to relocate the people living where the reservoirs are planned In February 2008 it was estimated that 40-80 million people worldwide had been physically displaced as a direct result of dam construction In many cases, no amount of compensation can replace ancestral and cultural attachments to places that have spiritual value to the displaced population Additionally, historically and culturally important sites can be flooded and lost Such problems have arisen at the Aswan Dam in Egypt between 1960 and 1980, the Three Gorges Dam in China, the Clyde Dam in New Zealand, and the Ilisu Dam in Turkey.
39 Failure hazard Because large conventional dammed-hydro facilities hold back large volumes of water, a failure due to poor construction, terrorism, or other cause can be catastrophic to downriver settlements and infrastructure Dam failures have been some of the largest man- made disasters in history Also, good design and construction are not an adequate guarantee of safety Dams are tempting industrial targets for wartime attack, sabotage and terrorism, such as Operation Chastise in World War II
40 The Banquio Damfailure in Southern China directly resulted in the deaths of 26,000 people, and another 145,000 from epidemics Millions were left homeless Also, the creation of a dam in a geologically inappropriate location may cause disasters such as 1963 disaster at Vajont Dam in Italy, where almost 2000 people died Smaller dams and micro hydro facilities create less risk, but can form continuing hazards even after being decommissioned For example, the small Kelly Barnes Dam in Georgia failed in 1967, causing 39 deaths with the Toccoa Flood, ten years after its power plant was decommissioned
41 Comparison with other methods of power generation Hydroelectricity eliminates the flue gas emissions from fossil fuel combustion, including pollutants such as sulfur dioxide, nitric oxide, carbon monoxide, dust, and mercury in the coal Hydroelectricity also avoids the hazards of coal mining and the indirect health effects of coal emissions Compared to nuclear power, hydroelectricity generates no nuclear waste, has none of the dangers associated with uranium mining, nor nuclear leaks Unlike uranium, hydroelectricity is also a renewable energy source Compared to wind farms, hydroelectricity power plants have a more predictable load factor If the project has a storage reservoir, it can generate power when needed, Hydroelectric plants can be easily regulated to follow variations in power demand.
42 Unlike fossil-fuelled combustion turbines, construction of a hydroelectric plant requires a long lead-time for site studies, hydrological studies, and environmental impact assessment Hydrological data up to 50 years or more is usually required to determine the best sites and operating regimes for a large hydroelectric plant Unlike plants operated by fuel, such as fossil or nuclear energy, the number of sites that can be economically developed for hydroelectric production is limited; in many areas the most cost-effective sites have already been exploited New hydro sites tend to be far from population centers and require extensive transmission lines Hydroelectric generation depends on rainfall in the watershed, and may be significantly reduced in years of low rainfall or snowmelt Long-term energy yield may be affected by climate change Utilities that primarily use hydroelectric power may spend additional capital to build extra capacity to ensure sufficient power is available in low water years
43 World hydroelectric capacity World renewable energy share (2008), with hydroelectricity more than 50% of all renewable energy sources
44 The ranking of hydro-electric capacity is either by actual annual energy production or by installed capacity power rating A hydro-electric plant rarely operates at its full power rating over a full year; the ratio between annual average power and installed capacity rating is the capacity factor The installed capacity is the sum of all generator nameplate power ratings. Sources came from BP Statistical Review - Full Report 2009 Brazil, Canada, New Zealand, Norway, Paraguay, Switzerland, and Venezuela are the only countries in the world where the majority of the internal electric energy production is from hydroelectric power Paraguay produces 100% of its electricity from hydroelectric dams, and exports 90% of its production to Brazil and to Argentina Norway produces 98–99% of its electricity from hydroelectric sources.
45 Ten of the largest hydroelectric producers as at 2009.   Country Annual hydroelectric production (TWh)TWh Installed capacity (GW)GW Capacity factor % of total capacity China 652.05196.790.3722.25 Canada 369.588.9740.5961.12 Brazil 363.869.0800.5685.56 United States 250.679.5110.425.74 Russia 167.045.0000.4217.64 Norway 140.527.5280.4998.25 India 115.633.6000.4315.80 Venezuela 85.9614.6220.6769.20 Japan 69.227.2290.377.21 Sweden 65.516.2090.4644.34
46 Hydropower, hydraulic power or water power is power that is derived from the force or energy of moving water, which may be harnessed for useful purposes Prior to the development of electric power, hydropower was used for irrigation, and operation of various machines, such as watermills, textile machines, sawmills, dock cranes, and domestic lifts Another method used a trompe to produce compressed air from falling water, which could then be used to power other machinery at a distance from the water In hydrology, hydropower is manifested in the force of the water on the riverbed and banks of a river. It is particularly powerful when the river is in flood The force of the water results in the removal of sediment and other materials from the riverbed and banks of the river, causing erosion and other alterations.
47 Waterwheels and mills Hydropower has been used for hundreds of years. In India, water wheels and watermills were built; in Imperial Rome, water powered mills produced flour from grain, and were also used for sawing timber and stone; in China, watermills were widely used since the Han Dynasty The power of a wave of water released from a tank was used for extraction of metal ores in a method known as hushing The method was first used at the Dolaucothi Gold Minein Wales from 75 AD onwards, but had been developed in Spain at such mines as Las Medulas Hushing was also widely used in Britain in the Medieval and later periods to extract lead and tin ores It later evolved into hydraulic mining when used during the California gold rush
48 In China and the rest of the Far East, hydraulically operated "pot wheel" pumps raised water into irrigation canals At the beginning of the Industrial revolution in Britain, water was the main source of power for new inventions such as Richard Arkwright's water frame Although the use of water power gave way to steam power in many of the larger mills and factories, it was still used during the 18th and 19th centuries for many smaller operations, such as driving the bellows in small blast furnaces (e.g. the Dyfi Furnace) and gristmills, such as those built at Saint Anthony Falls, which uses the 50-foot (15 m) drop in the Mississippi River In the 1830s, at the peak of the canal-building era, hydropower was used to transport barge traffic up and down steep hills using inclined plane railroads.
49 Hydraulic power pipes Hydraulic power networks also existed, using pipes carrying pressurized liquid to transmit mechanical power from a power source, such as a pump, to end users These were extensive in Victorian cities in the United Kingdom A hydraulic power network was also in use in Geneva, Switzerland. The world famous Jet d'Eau was originally the only over pressure valve of this network
50 Compressed air hydro Where there is a plentiful head of water it can be made to generate compressed air directly without moving parts A falling column of water is mixed with air bubbles generated through turbulence at the inlet This is allowed to fall down a shaft into a subterranean chamber where the air separates from the water The weight of falling water compresses the air in the top of the chamber A submerged outlet from the chamber allows water to flow to the surface at a lower height than the intake An outlet in the roof of the chamber supplies the compressed air to the surface A facility on this principal was built on the Montreal River at Ragged Shutes near Cobalt, Ontario in 1910 and supplied 5,000 horsepower to nearby mines.  
51 A conventional dammed-hydro facility (hydroelectric dam) is the most common type of hydroelectric power generation
52 A Pelamis wave device under test at the European Marine Energy Centre (EMEC), Orkney, Scotland
53 Marine Power Marine current power, which captures the kinetic energy from marine currents Osmotic power, which channels river water into a container separated from sea water by a semi-permeable membrane Ocean thermal energy, which exploits the temperature difference between deep and shallow waters Tidal power, which captures energy from the tides in horizontal direction. Also a popular form of hydroelectric power generation Tidal stream power, usage of stream generators, somewhat similar to that of a wind turbine Tidal barrage power, usage of a tidal dam Dynamic tidal power, utilizing large areas to generate head. Wave power, the use ocean surface waves to generate power.
54 Calculating the amount of available power A hydropower resource can be measured according to the amount of available power, or energy per unit time. In large reservoirs, the available power is generally only a function of the hydraulic head and rate of fluid flow. In a reservoir, the head is the height of water in the reservoir relative to its height after discharge. Each unit of water can do an amount of work equal to its weight times the head. The amount of energy, E, released when an object of mass m drops a height h in a gravitational field of strength g is given by The energy available to hydroelectric dams is the energy that can be liberated by lowering water in a controlled way In these situations, the power is related to the mass flow rate.
55 Substituting P for E ⁄ t and expressing m ⁄ t in terms of the volume of liquid moved per unit time (the rate of fluid flow, φ) and the density of water, we arrive at the usual form of this expression: or A simple formula for approximating electric power production at a hydroelectric plant is: P = hrgk where P is Power in kilowatts, h is height in meters, r is flow rate in cubic meters per second, g is acceleration due to gravity of 9.8 m/s2, and k is a coefficient of efficiency ranging from 0 to 1 Efficiency is often higher with larger and more modern turbines
56 Some hydropower systems such as water wheels can draw power from the flow of a body of water without necessarily changing its height. In this case, the available power is the kinetic energy of the flowing water. where v is the speed of the water, or with where A is the area through which the water passes, also Over-shot water wheels can efficiently capture both types of energy
57 Water turbine Kaplan turbine and electrical generator cut-away view.
59 Swirl The word turbine was introduced by the French engineer Claude Bourdin in the early 19th century and is derived from the Latin word for "whirling" or a "vortex“ The main difference between early water turbines and water wheels is a swirl component of the water which passes energy to a spinning rotor This additional component of motion allowed the turbine to be smaller than a water wheel of the same power They could process more water by spinning faster and could harness much greater heads Later, impulse turbines were developed which didn't use swirl
60 The earliest known water turbines date to the Roman Empire Two helix-turbine mill sites of almost identical design were found at Chemtou and Testier, modern-day Tunisia, dating to the late 3rd or early 4th century AD The horizontal water wheel with angled blades was installed at the bottom of a water-filled, circular shaft The water from the mill-race entered tangentially the pit, creating a swirling water column which made the fully submerged wheel act like a true turbine Jan Andrei Segner developed a reactive water turbine in the mid-18th century It had a horizontal axis and was a precursor to modern water turbines. It is a very simple machine that is still produced today for use in small hydro sites Segner worked with Euler on some of the early mathematical theories of turbine design.
61 In 1826, Benoit Fournerior developed an outward-flow turbine. This was an efficient machine (~80%) that sent water through a runner with blades curved in one dimension. The stationary outlet also had curved guides In 1844, Uriah A. Boyden developed an outward flow turbine that improved on the performance of the Fourneyron turbine. Its runner shape was similar to that of a Francis turbine In 1849, James B. Francis improved the inward flow reaction turbine to over 90% efficiency He also conducted sophisticated tests and developed engineering methods for water turbine design The Francis turbine, named for him, is the first modern water turbine It is still the most widely used water turbine in the world today The Francis turbine is also called a radial flow turbine, since water flows from the outer circumference towards the centre of runner.
62 Francis turbine The Francis turbine is a type of water turbine that was developed by James B. Francis in Lowell, Massachusetts It is an inward-flow reaction turbine that combines radial and axial flow concepts Francis turbines are the most common water turbine in use today They operate in a head range of ten meters to six hundred and fifty meters and are primarily used for electrical power production The power output ranges from 10 to 750MW, mini-hydro excluded Runner diameters are between 1 and 10 meters The speed range of the turbine is from 83 to 1000 rpm Medium size and larger Francis turbines are most often arranged with a vertical shaft Vertical shaft may also be used for small size turbines, but normally they have horizontal shaft
65 Water wheels have been used historically to power mills of all types, but they are inefficient. Nineteenth-century efficiency improvements of water turbines allowed them to compete with steam engines (wherever water was available) In 1826 Benoit Fourneyron developed a high efficiency (80%) outward-flow water turbine Water was directed tangentially through the turbine runner, causing it to spin Jean-Victor Poncelet designed an inward-flow turbine in about 1820 that used the same principles. S. B. Howd obtained a U.S. patent in 1838 for a similar design In 1848 James B. Francis, while working as head engineer of the Locks and Canals company in the water-powered factory city of Lowell, Massachusetts, improved on these designs to create a turbine with 90% efficiency He applied scientific principles and testing methods to produce a very efficient turbine design More importantly, his mathematical and graphical calculation methods improved turbine design and engineering His analytical methods allowed confident design of high efficiency turbines to exactly match a site's flow conditions
67 The Francis turbine is a reaction turbine, which means that the working fluid changes pressure as it moves through the turbine, giving up its energy A casement is needed to contain the water flow The turbine is located between the high-pressure water source and the low-pressure water exit, usually at the base of a dam The inlet is spiral shaped Guide vanes direct the water tangentially to the turbine wheel, known as a runner This radial flow acts on the runner's vanes, causing the runner to spin The guide vanes (or wicket gate) may be adjustable to allow efficient turbine operation for a range of water flow conditions
68 Francis Turbine (exterior view) attached to a generator
69 As the water moves through the runner, its spinning radius decreases, further acting on the runner For an analogy, imagine swinging a ball on a string around in a circle; if the string is pulled short, the ball spins faster due to the conservation of angular momentum This property, in addition to the water's pressure, helps Francis and other inward-flow turbines harness water energy efficiently At the exit, water acts on cup-shaped runner features, leaving with no swirl and very little kinetic or potential energy The turbine's exit tube is shaped to help decelerate the water flow and recover the pressure
70 Application Francis turbines may be designed for a wide range of heads and flows This, along with their high efficiency, has made them the most widely used turbine in the world Francis type units cover a head range from 20 meters to 700 meters, and their output power varies from just a few kilowatts up to one gigawatt Large Francis turbines are individually designed for each site to operate at the highest possible efficiency, typically over 90% In addition to electrical production, they may also be used for pumped storage, where a reservoir is filled by the turbine (acting as a pump) during low power demand, and then reversed and used to generate power during peak demand
71 Inward flow water turbines have a better mechanical arrangement and all modern reaction water turbines are of this design As the water swirls inward, it accelerates, and transfers energy to the runner. Water pressure decreases to atmospheric, or in some cases subatmospheric, as the water passes through the turbine blades and loses energy Around 1890, the modern fluid bearing was invented, now universally used to support heavy water turbine spindles As of 2002, fluid bearings appear to have a mean time between failures of more than 1300 years. Around 1913, Viktor Kaplan created the Kaplan turbine, a propeller-type machine It was an evolution of the Francis turbine but revolutionized the ability to develop low-head hydro sites.
72 Figure from Pelton's original patent (October 1880) A new concept
73 All common water machines until the late 19th century (including water wheels) were basically reaction machines; water pressure head acted on the machine and produced work. A reaction turbine needs to fully contain the water during energy transfer In 1866, California millwright Samuel Knight invented a machine that took the impulse system to a new level Inspired by the high pressure jet systems used in hydraulic mining in the gold fields, Knight developed a bucketed wheel which captured the energy of a free jet, which had converted a high head (hundreds of vertical feet in a pipe or penstock) of water to kinetic energy This is called an impulse or tangential turbine The water's velocity, roughly twice the velocity of the bucket periphery, does a u-turn in the bucket and drops out of the runner at low velocity.
74 In 1879, Lester Pelton (1829-1908), experimenting with a Knight Wheel, developed a double bucket design, which exhausted the water to the side, eliminating some energy loss of the Knight wheel which exhausted some water back against the center of the wheel In about 1895, William Doble improved on Pelton's half- cylindrical bucket form with an elliptical bucket that included a cut in it to allow the jet a cleaner bucket entry This is the modern form of the Pelton turbine which today achieves up to 92% efficiency Pelton had been quite an effective promoter of his design and although Doble took over the Pelton company he did not change the name to Doble because it had brand name recognition Turgo and Crossflow Turbineswere later impulse designs.
75 Theory of operation Flowing water is directed on to the blades of a turbine runner, creating a force on the blades Since the runner is spinning, the force acts through a distance (force acting through a distance is the definition of work) In this way, energy is transferred from the water flow to the turbine Water turbines are divided into two groups; reaction turbines and impulse turbines The precise shape of water turbine blades is a function of the supply pressure of water, and the type of impeller selected.
76 Reaction turbines Reaction turbines are acted on by water, which changes pressure as it moves through the turbine and gives up its energy They must be encased to contain the water pressure (or suction), or they must be fully submerged in the water flow Newton's third law describes the transfer of energy for reaction turbines. Most water turbines in use are reaction turbines and are used in low (<30m/98 ft) and medium (30-300m/98– 984 ft)head applications. In reaction turbine pressure drop occurs in both fixed and moving blades.
77 Impulse turbines Impulse turbines change the velocity of a water jet. The jet pushes on the turbine's curved blades which changes the direction of the flow The resulting change in momentum (impulse) causes a force on the turbine blades. Since the turbine is spinning, the force acts through a distance (work) and the diverted water flow is left with diminished energy Prior to hitting the turbine blades, the water's pressure (potential energy) is converted to kinetic energy by a nozzle and focused on the turbine No pressure change occurs at the turbine blades, and the turbine doesn't require a housing for operation Newton's second law describes the transfer of energy for impulse turbines Impulse turbines are most often used in very high (>300m/984 ft) head applications
78 Newton’s Laws of Motion Newton's First Law of Motion: I. Every object in a state of uniform motion tends to remain in that state of motion unless an external force is applied to it. Newton's Second Law of Motion: II. The relationship between an object's mass m, its acceleration a, and the applied force F is F = ma. Acceleration and force are vectors in this law the direction of the force vector is the same as the direction of the acceleration vector. Newton's Third Law of Motion: III. For every action there is an equal and opposite reaction.
79 Power The power available in a stream of water is; where: P = power (J/s or watts) η = turbine efficiency ρ = density of water (kg/m³) g = acceleration of gravity (9.81 m/s²) h = head (m) For still water, this is the difference in height between the inlet and outlet surfaces Moving water has an additional component added to account for the kinetic energy of the flow The total head equals the pressure head plus velocity head. = flow rate (m³/s)
80 Pumped storage Some water turbines are designed for pumped storage hydroelectricity They can reverse flow and operate as a pump to fill a high reservoir during off-peak electrical hours, and then revert to a turbine for power generation during peak electrical demand This type of turbine is usually a Deriaz or Francis in design Efficiency Large modern water turbines operate at mechanical efficiencies greater than 90% (not to be confused with thermodynamic efficiency).
81 Types of water turbines Various types of water turbine runners. From left to right: Pelton Wheel, two types of Francis Turbine and Kaplan Turbine
82 Reaction turbines: Francis Kaplan, Propeller, Bulb, Tube, Straflo Tyson Gorlov Impulse turbine Waterwheel Pelton Turgo Michell-Banki (also known as the Crossflow or Ossberger turbine) Jonval turbine Reverse overshot water-wheel Archimedes' screw turbine
84 Turbine selection is based mostly on the available water head, and less so on the available flow rate In general, impulse turbines are used for high head sites, and reaction turbines are used for low head siteslow head Kaplan turbines with adjustable blade pitch are well-adapted to wide ranges of flow or head conditions, since their peak efficiency can be achieved over a wide range of flow conditions. Small turbines (mostly under 10 MW) may have horizontal shafts, and even fairly large bulb-type turbines up to 100 MW or so may be horizontal Very large Francis and Kaplan machines usually have vertical shafts because this makes best use of the available head, and makes installation of a generator more economical Pelton wheels may be either vertical or horizontal shaft machines because the size of the machine is so much less than the available head Some impulse turbines use multiple water jets per runner to increase specific speed and balance shaft thrust.
85 Typical range of heads Hydraulic wheel turbine Archimedes' screw turbine Kaplan_________________ Francis 10 < H < 350 Pelton 50 < H < 1300 Turgo 50 < H < 250Hydraulic wheel turbineArchimedes' screwKaplanFrancisPeltonTurgo 0.2 < H < 4 (H = head in m) 1 < H < 10 2 < H < 40
86 Specific speed The specific speed n s of a turbine characterizes the turbine's shape in a way that is not related to its size This allows a new turbine design to be scaled from an existing design of known performance The specific speed is also the main criteria for matching a specific hydro site with the correct turbine type The specific speed is the speed with which the turbine turns for a particular discharge Q, with unit head and thereby is able to produce unit power.
87 Affinity laws Affinity Laws allow the output of a turbine to be predicted based on model tests A miniature replica of a proposed design, about one foot (0.3 m) in diameter, can be tested and the laboratory measurements applied to the final application with high confidence Affinity laws are derived by requiring similitude between the test model and the application Flow through the turbine is controlled either by a large valve or by wicket gates arranged around the outside of the turbine runner Differential head and flow can be plotted for a number of different values of gate opening, producing a hill diagram used to show the efficiency of the turbine at varying conditions
88 Runaway speed The runaway speed of a water turbine is its speed at full flow, and no shaft load The turbine will be designed to survive the mechanical forces of this speed The manufacturer will supply the runaway speed rating.
89 Environmental impact Water turbines are generally considered a clean power producer, as the turbine causes essentially no change to the water They use a renewable energy source and are designed to operate for decades They produce significant amounts of the world's electrical supply Historically there have also been negative consequences, mostly associated with the dams normally required for power production Dams alter the natural ecology of rivers, potentially killing fish, stopping migrations, and disrupting peoples' livelihoods.
90 For example, American Indian tribes in the Pacific Northwest had livelihoods built around salmon fishing, but aggressive dam-building destroyed their way of life Dams also cause less obvious, but potentially serious consequences, including increased evaporation of water (especially in arid regions), build up of silt behind the dam, and changes to water temperature and flow patterns Some people believe that it is possible to construct hydropower systems that divert fish and other organisms away from turbine intakes without significant damage or loss of power; historical performance of diversion structures have been poor. n the United States, it is now illegal to block the migration of fish, for example the endangered great white sturgeon in North America, so fish ladders must be provided by dam builders The actual performance of fish ladders is often poor