Describe construction and working of high head micro hydro plant.
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Answer :
Construction of hydroelectric power plant
Dam and Reservoir: The dam is constructed on a large river in hilly areas to ensure sufficient water storage at height. The dam forms a large reservoir behind it. The height of water level (called as water head) in the reservoir determines how much of potential energy is stored in it.
Intake gate or Control Gate: Water from the reservoir is allowed to flow through the penstock to the turbine. The amount of water which is to be released in the penstock can be controlled by a control gate. When the control gate is fully opened, maximum amount of water is released through the penstock.
Penstock: A penstock is a huge steel pipe which carries water from the reservoir to the turbine. Potential energy of the water is converted into kinetic energy as it flows down through the penstock due to gravity.
Water Turbine: Water from the penstock is taken into the water turbine. The turbine is mechanically coupled to an electric generator. Kinetic energy of the water drives the turbine and consequently the generator gets driven. There are two main types of water turbine; (i) Impulse turbine and (ii) Reaction turbine. Impulse turbines are used for large heads and reaction turbines are used for low and medium heads.
Impulse Turbines
Impulse turbines, which have the least complex design, are most commonly used for high-head microhydro systems. They rely on the velocity of water to move the turbine wheel, which is called the runner. The most common types of impulse turbines include the Pelton wheel and the Turgo wheel.
Reaction Turbines
Reaction turbines, which are highly efficient, depend on pressure rather than velocity to produce energy. All blades of the reaction turbine maintain constant contact with the water. These turbines are often used in large-scale hydropower sites.Because of their complexity and high cost, reaction turbines aren't usually used for microhydropower projects.
Generator: A generator is mounted in the power house and it is mechanically coupled to the turbine shaft. When the turbine blades are rotated, it drives the generator and electricity is generated which is then stepped up with the help of a transformer for the transmission purpose.
Surge Tank: Surge tanks are usually provided in high or medium head power plants when considerably long penstock is required. A surge tank is a small reservoir or tank which is open at the top. It is fitted between the reservoir and the power house. The water level in the surge tank rises or falls to reduce the pressure swings in the penstock. When there is sudden reduction in load on the turbine, the governor closes the gates of the turbine to reduce the water flow. This causes pressure to increase abnormally in the penstock. This is prevented by using a surge tank, in which the water level rises to reduce the pressure. On the other hand, the surge tank provides excess water needed when the gates are suddenly opened to meet the increased load demand.
Electrical equipment: The electrical equipment of a hydro electric power station includes alternators, transformers, circuit breakers and other switching and protective devices.
Diagram -
Working of hydro power plant
In Hydropower plant, dam acts as a strong wall to get the water level high in the reservoir, thus increasing its potential energy. Height difference in the level of reservoir and penstock, is the main reason behind all the pressure force that would strike the turbine and thus generate the requiredpower.
Once the control gates are opened the water through penstock travel to the turbine. Main reasonbehind having a surge tank is to prevent penstock from water hammering. It’s a really very important part as, we have a valve just before the turbine which control the flow of water entering the turbine according to the load at the turbine.
But the opening and closing of this valve is controlled directly by the governor action. Governor acts according to the load at the turbine. So as the load at the turbine decreases gates slam shut in a short period of time. This would cause pressure to rise in penstock, thus could destroy penstock, but due to surge tank this pressure is compensated thus solving the problem. Surge tank also helps to cover up the air gap when load on the turbine increases instantly. It feed water to keep the flow of water striking turbine consistent and smooth, thus preventing the fluctuations in power output.
Trash rack is there to remove all the impurities from the water going to turbine. It reduces the wear and tear of the turbine thus increasing the turbine life.
Water strikes the turbine blades, converting the pressure energy of water into mechanical energy, which is further gets converted into electrical energy by generator. This voltage of the electricity is increased with stepup transformer and we are all set to transfer this high voltage electricity to nearest power grid through transmission lines.