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Hydro Electric Power Plants

Hydro-electric Power Plants capture the energy released by water falling through a vertical distance, and transform this energy into useful electricity. In general, falling water is channeled through a turbine which converts the water's energy into mechanical power. The rotation of the water turbines is transferred to a generator, which produces electricity. The amount of electricity which can be generated at a hydro-electric plant is dependent upon two factors. These factors are :

the vertical distance through which the water falls, called the "head", and
The flow rate measured as volume per unit time.

The electricity produced is proportional to the product of the head and the rate of flow. The following is an equation, which may be used to roughly determine the amount of electricity, which can be generated, by a potential hydro-electric power site:

POWER (kW) = 5.9 x FLOW x HEAD
In this equation, FLOW is measured in cubic meters per second and HEAD is measured in meters. Based on the facts presented above, hydro-electric power plants can generally be divided into two categories. "High head" power plants are the most common and generally utilize a dam to store water at an increased elevation. The use of a dam to impound water also provides the capability of storing water during rainy periods and releasing it during dry periods. This results in the consistent and reliable production of electricity, able to meet demand. Heads for this type of power plant may be greater than 1000 m. Most large hydro-electric facilities are of the high head variety. High head plants with storage are very valuable to electric utilities because they can be quickly adjusted to meet the electrical demand on a distribution system. "Low head" hydro-electric plants are power plants which generally utilize heads of only a few meters or less. Power plants of this type may utilize a low dam or weir to channel water, or no dam and simply use the "run of the river". Run of the river generating stations cannot store water, thus their electric output varies with seasonal flows of water in a river. A large volume of water must pass through a low head hydro plant's turbines in order to produce a useful amount of power. Hydroelectric facilities with a capacity of less than about 25 MW (1 MW = 1,000,000 Watts) are generally referred to as "small hydro", although hydro-electric technology is basically the same regardless of generating capacity.

P = u.g.H.Q, where u = overall coefficient of efficiency.
Most conventional hydropower plants include six major components.

Dam. Controls the flow of water and increases the elevation to create the head the reservoir that is formed is, in effect, stored energy.
Penstock. Carries water from the reservoir to the turbine in a power plant.
Turbine. Turned by the force of water pushing against its blades.
Generator. Connects to the turbine and rotates to produce the electrical energy.
Transmission lines. Conduct electricity from the hydropower plant to the electric distribution system

The principal advantages of using hydropower are its large renewable domestic resource base, the absence of polluting emissions during operation, its capability in some cases to respond quickly to utility load demands, and its very low operating costs. Disadvantages can include high initial capital cost and potential site-specific and cumulative environmental impacts. Potential environmental impacts of hydropower projects include altered flow regimes below storage reservoirs or within diverted stream reaches, water quality degradation, mortality of fish that pass through hydroelectric turbines, blockage of upstream fish migration, and flooding of terrestrial ecosystems by new impoundments. However, in many cases, proper design and operation of hydropower projects can mitigate these impacts. Hydroelectric projects also include beneficial effects such as recreation in reservoirs or in tailwaters below dams


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