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To browse Academia. Skip to main content. You're using an out-of-date version of Internet Explorer. Log In Sign Up. Denis Den. Small hydro power: technology and current status. Renewable and Sustainable Energy Reviews 6 — www. This paper summarises the different small hydro technologies, new innovations being developed, and the barriers to further development. Introduction Hydropower on a small-scale is one of the most cost-effective energy technologies to be considered for rural electrification in less developed countries.
Internet: www. E-mail address: oliver. Small hydro technology is extremely robust systems can last for 50 years or more with little maintenance and is also one of the most environmentally benign energy technologies available.
The development of hydro-electricity in the 20th century was usually associated with the building of large dams. Hundreds of massive barriers of concrete, rock and earth were placed across river valleys world-wide to create huge artificial lakes. While they created a major, reliable power supply, plus irrigation and flood control benefits, the dams necessarily flooded large areas of fertile land and displaced many thousands of local inhabitants.
In many cases, rapid silting up of the dam has since reduced its productivity and lifetime. There are also numerous environmental prob- lems that can result from such major interference with river flows. The civil works purely serve the function of regulating the level of the water at the intake to the hydro-plant. Therefore run-of-river installations do not have the same kinds of adverse effect on the local environment as large hydro. A maximum of 10 MW is the most widely accepted value worldwide, although the definition in China stands officially at 25 MW.
These are arbitrary divisions and many of the principles involved apply to both smaller and larger schemes. Historical background Hydropower started with the wooden waterwheel. Waterwheels of various types had been in use in many parts of Europe and Asia for some 2, years, mostly for milling grain.
Improved engineering skills during the 19th century, combined with the need to develop smaller and higher speed devices to generate electricity, led to the development of modern- day turbines.
Towards the end of that century many mills were replacing their waterwheels with turbines, and governments were beginning to focus on how they could exploit hydropower for large-scale supply of electricity. As illustrated in Fig. Exploited hydro potential by continent . The global small hydro potential is believed to be in excess of GW. China alone has developed more than 15 GW, and plans to develop a further 10 GW in the current decade.
Small hydro provides over 8 GW of capacity and there is an estimated 18 GW of further small hydro potential, including refurbishment projects. The UK has MW of small hydro capacity operating from approximately sites. Basics Hydro-turbines convert water pressure into mechanical shaft power, which can be used to drive an electricity generator, or other machinery.
The power available is proportional to the product of pressure head and volume flow rate. Figure 2 and Figure 3 illustrate a typical small hydro scheme. Water is taken from the river by diverting it through an intake at a weir. The weir is a man-made barrier across the river which maintains a continuous flow through the intake.
Before descending to the turbine, the water passes through a settling tank or forebay in which the water is slowed down sufficiently for suspended particles to settle out. The forebay is usually protected by a rack of metal bars a trash rack which filters out water-borne debris which might damage the turbine such as stones, timber, or man-made litter.
Small hydro site layout. A pressure pipe, known as a penstock, conveys the water from the forebay to the turbine. All installations need to have a valve or sluice gate at the top of the penstock which can be closed when the turbine needs to be shutdown and emptied of water for maintenance.
When this valve is closed, the water is diverted back to the river down a spillway. Technology A turbine converts the energy from falling water into rotating shaft power.
The selection of the best turbine for any particular hydro site depends upon the site characteristics, the dominant ones being the head and flow available. Selection also depends on the desired running speed of the generator or other device loading the turbine.
Other considerations, such as whether the turbine will be expected to produce power under reduced flow conditions, also play an important role in the selection. All turbines have a power-speed characteristic, and an efficiency-speed characteristic. They will tend to run most efficiently at a particular speed, head and flow. Classification Turbines can be crudely classified as high-head, medium-head, or low-head machines, as shown in Table 1.
This 1. The main reason that different types of turbine are used at different heads is that electricity generation requires a shaft speed as close as possible to rpm to minimize the speed change between the turbine and the generator.
The approximate ranges of head, flow and power applicable to the different turbine types are summarised in the chart of Fig. These are approxi- mate and dependent on the precise design of each manufacturer. Turbines are also divided by their principle of operation and can be either impulse or reaction turbines. The rotor of the reaction turbine is fully immersed in water and is enclosed in a pressure casing. The runner blades are profiled so that pressure differences across them impose lift forces, akin to those on aircraft wings, which cause the runner to rotate.
In contrast an impulse turbine runner operates in air, driven by a jet or jets of water, and the water remains at atmospheric pressure before and after making contact with the runner blades.
Impulse turbines There are 3 main types of impulse turbine in use: the Pelton, the Turgo, and the Crossflow the latter is also known as the Banki turbine. The Pelton Turbine Figure 5 consists of a wheel with a series of split buckets set around its rim; a high velocity jet of water is directed tangentially at the wheel.
Nearly all the energy of the water goes into propelling the bucket and the deflected water falls into a discharge channel below. Therefore the flow rate is not limited by Fig. Head-flow ranges of small hydro turbines .
Pelton Turbine. Turgo Turbine. As a consequence, a Turgo turbine can have a smaller diameter runner than a Pelton for an equivalent power. A jet of water enters the top of the rotor through the curved blades, emerging on the far side of the rotor by passing through the blades a 2nd time.
The shape of the blades is such that on each passage through the periphery of the rotor the water transfers some of its momentum, before falling away with little residual energy. Reaction turbines Reaction turbines exploit the oncoming flow of water to generate hydrodynamic lift forces to propel the runner blades. They are distinguished from the impulse type by having a runner that always functions within a completely water-filled casing.
The draft tube slows the discharged water and reduces the static pressure below the runner and thereby increases the effective head. The two main types of reaction turbine are the propeller with Kaplan variant and Francis turbines. Propeller-type turbines Figure 8 are similar in principle to the propeller of a ship, but operating in reversed mode. Various configurations of propeller turbine exist; a key feature is that for good efficiency the water needs to be given some swirl before entering the turbine runner.
With good design the swirl is absorbed by the runner and the water that emerges flows straight into the draft tube with little residual angular momentum.
Methods for adding inlet swirl include the use of a set Fig. Crossflow Turbine. Tube-type Propeller Turbine. When guide vanes are used, these are often adjustable so as to vary the flow admitted to the runner. In some cases the blades of the runner can also be adjusted, in which case the turbine is called a Kaplan. The mechanics for adjusting turbine blades and guide vanes can be costly and tend to be more affordable for large systems, but can greatly improve efficiency over a wide range of flows.
The Francis turbine Figure 9 is essentially a modified form of propeller turbine in which water flows radially inwards into the runner and is turned to emerge axially. The runner is most commonly mounted in a spiral casing with internal adjustable guide vanes. Reaction turbines require more sophisticated fabrication than impulse turbines because they involve the use of more intricately profiled blades together with care- fully profiled casings.
Fabrication constraints therefore make these turbines less attractive for use in micro-hydro in developing countries. Nevertheless, because low- head sites are far more numerous and closer to where the power is needed, work is being undertaken to develop propeller machines which are simpler to construct.
Relative efficiencies A significant factor in the comparison of different turbine types is their relative efficiencies both at their design point and at reduced flows.
Typical efficiency curves  are shown in Fig. Francis Turbine. Speed control Many small hydro stations in developing countries are not connected to a national grid, but supply a local town or village.
In this case there is no strong grid to hold the generator to the correct frequency 50 or 60 Hz and an effective speed regulation system is important to ensure that the voltage and frequency remain constant as the electrical load changes through the day.
In some cases a valve is automatically driven by a governing mechanism which adjusts the flow to the turbine to meet variations in power demand.
In other cases the turbine always runs at full power and speed control is achieved by adjusting the electrical power output rather than the water power input. In this situation excess electrical power is switched in and out of a ballast load by an Electronic Load Controller or ELC.
Part-flow efficiencies . Economics High head hydro generally provides the most cost-effective projects, since the higher the head, the less water is required for a given amount of power, so smaller and hence less costly equipment is needed. Therefore, in mountainous regions even quite small streams if used at high heads can yield significant power levels at attract- ively low costs.
However high head sites tend to be in areas of low population density where the demand for electricity is small, and long transmission distances to the main centres of population can nullify the low cost advantages of remote high head systems. Also high head sites are relatively rare, with most of the best ones in Europe and other developed regions being already exploited. Therefore the greatest scope for expanding the use of small hydro is increasingly with low head sites.
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Previous issue Next issue. View all abstracts. The international Scientific Electric Power Conference held annually at the Institute of Energy and Transport System, Peter the Great Saint Petersburg Polytechnic University, has created a platform for summarizing research in the technical fields of knowledge in higher educational institutions, research institutes, large industrial enterprises, research and production associations and individual scientists. The aim of the conference is to contribute to informing scientists and practitioners about the most promising areas of research and achievements in the field of electric power industry. Petersburg, Russia, on 23 rd and 24 th of May,
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The company built upon several predecessor companies efforts to construct a canal used for hydraulic mill power. The purchase also included the water rights from above the upper rapids to below the Falls. In , Caleb Smith Woodhull and his associates purchased the land and the water rights from the heirs of the Porter brothers with the intention to build a canal, and in formed the " Niagara Falls Hydraulic Company.
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ГЛАВА 53 Токуген Нуматака лежал на массажном столе в своем кабинете на верхнем этаже. Личная массажистка разминала затекшие мышцы его шеи. Погрузив ладони в складки жира на плечах шефа, она медленно двигалась вниз, к полотенцу, прикрывавшему нижнюю часть его спины.
Ее руки спускались все ниже, забираясь под полотенце. Нуматака почти ничего не замечал.
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