Hydroelectric Engineering Principles
How the Potential Energy of Water is Converted to Electricity
Sep 20, 2009
Hydroelectric engineering is concerned with the design, development, and maintenance of power plants that convert the potential energy of water into electricity. Hydroelectric power generation accounts for 20% of worldwide electricity production and over 80% of electricity generated from renewable resources.
Hydroelectric Power Basics
The energy generation capacity of a hydroelectric power plant is based on several variables. The power generation potential of a hydroelectric power plant can be estimated using the formula: P = ρhrgk, where:
- P is the estimated power generation
- ρ is the density of the water
- h is the height of the water in the reservoir, also called the head
- r is the flow rate of the water
- k is an efficiency factor, based on the efficiency of the turbine
Water from the reservoir enters the hydroelectric power plant through an intake in the upstream side of the dam into the penstock, a tube that connects the reservoir to the turbine. The water generally has to pass through a grate or screen to prevent dirt, rocks, or other solids from entering the penstock and damaging the turbine. The water passes through the turbine, rotating it and generating electricity. The water then exits the downstream side of the facility to return to the waterway.
Types of Turbines Used in Hydroelectric Power Plants
Depending on the amount of head and the requirements of the facility, either impulse turbines or reaction turbines can be used.
- Impulse turbines feed the water flow through a nozzle and into the turbine. The pressure of the head acts on the turbine to produce work. The turbine blades are curved like cups, and are designed to capture as much of the kinetic energy of the water jet as possible. A needle valve is used to meter the water flow to match production requirements. Impulse turbine designs include Pelton, Turgo, and Crossflow. Impulse turbines are generally used in very high head applications.
- Reaction turbines are reacted on by the water input, which loses pressure as it passes through the turbine. Reaction turbines are sealed or submerged within the water to maintain the pressure within the system. Reaction turbine designs include Francis, Kaplan, and Tyson designs. Reaction turbines are used in low to medium head applications.
There are several designs of each type of turbines in use in hydroelectric power plants, and efficiencies can approach 95%. The efficiencies of hydroelectric power generation, combined with zero emissions and low overall maintenance costs make hydroelectric power generation an extremely attractive electricity generation option.
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