Hydropower is considered to be a renewable energy source because it uses the continuous flow of water without using up the water resource. It is also nonpolluting, since it does not rely on burning fossil fuels. Hydropower is currently the leading renewable energy source in the United States. In 2009, it accounted for about 63 percent of all other renewable energy sources, such as wind, solar, and biomass. Reclamation is the nation’s second largest producer of hydroelectric power, with 58 hydroelectric power plants and 194 generating units in operation and an installed capacity of 14,693 MW. Almost all suitable sites for dams have already been developed, so there is not much scope for further growth in water power. However, there are numerous areas where research can lead to increases in the efficiency and reliability of hydroelectric plants and decreases in maintenance costs. Presently, wind and solar energy are growing at a rapid rate, and in a near future they will be the major sources of renewable energy for production of electric power.
The hydroelectric power plants usually require a dam to store water, a pen-stock for delivering the falling water, electric generators, a valve house which contains the main sluice valves, automatic isolating valves, and related control equipments. Also, a surge tank is located just before the valve house to protect the penstock from a pressure surge, called water hammer, in case the turbine gates are suddenly closed. In addition to electric energy production, most dams in the United States are built for other uses, including recreation, irrigation, flood control, and public water supply. A schematic diagram of a hydroelectric power plant is shown in Figure 1.6.
Figure 1.6
converts mechanical energy into electrical energy. After passing through the turbine, the water reenters the river on the downstream side of the dam. The most significant operating characteristics of hydropower plants are rapid start-up and loading, long life, and low operating and maintenance costs. Hydraulic turbines, particularly those operating with a low pressure, operate at low speed. Their generators are usually salient-type rotor with many poles. To maintain the generator voltage frequency constant, the turbine must spin the generator at a constant speed given by
n = 120f / p
where f is the generated voltage frequency and p is the number of poles of the generator.
The potential energy of the water in the reservoir is proportional to the mass of water and the difference in height between the water impoundment and the water outflow. This height difference is called the head or effective head. That is, P.E = mgh. The mass of water is its volume times its density. Therefore, P.E =
volume x p gh and the available hydro power becomes
Pw = P.E / t
Pw = volume x pgh / t
Pw = qpgh W
p = density of water in kg / m3 (1000 kg/m3)
q = rate of flow of water in m3 / s
h = effective head of water in m
g = acceleration of gravity (9,81 m/s2)
With the knowledge of the above g and p values,
P = 9,81.q.h
Let's get n is an overall efficiency of the hydropower plant, the electrical power output in kW is
Po = 9,81.q.h.n
where n is
n = np.nt.ng
np is penstock efficiency
nt is turbine efficiency
ng is generator efficiency
Turbines will be explained other edition of Power Plant
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