Regarded as a green energy, hydroelectric energy comes from the power of flowing water, a renewable resource, to generate electricity. Hydroelectric stations don't create pollution or contaminate the environment. In the United States, about 96 percent of the renewable energy and about 10 percent of the overall electricity produced comes from hydroelectric energy. Elements of a hydroelectric station are the flowing water, a turbine, a generator and transmission lines that conduct the electricity to end-point users.
Forms of Energy
Energy cannot be created nor destroyed in nature, but it can be transformed from one form into another. A hydroelectric station uses the moving, or kinetic, energy of flowing water to turn the propeller-like blades of a turbine, transforming it into mechanical energy. Inside the generator, the mechanical energy is changed into electricity when the turbine turns the generator rotor. Most large hydroelectric stations are located near dams, which create a body of water that gets released from a height to flow past the turbine blades.
Usually located underneath the power plant, the hydroelectric turbine has an intake valve, also called a penstock, that connects it to the source of falling water. The valve directs the water onto the curved blades of the turbine, making them spin around. As the water passes through the turbine blades, it leaves through the exit valve, discharging to a lower body of water. The turbine blades are connected to a central shaft, which turns the rotors within the turbine generators in the power plant. Sometimes the discharge water is reused by pumping water from the lower pond back up to the water that feeds into the intake valve.
Hydroelectric generators change mechanical energy into electrical energy using the principles discovered by English scientist Michael Faraday. In 1831, he described electromagnetic induction, which allowed the development of electricity into a useful tool rather than just a scientific curiosity. His experiment involved making a coil of wire by wrapping it around a paper cylinder. Connecting the wire coil to a galvanometer, which detects electrical currents, he moved a magnet back and forth inside the paper cylinder. As the magnet moved, the galvanometer recorded an induced electric current in the wire coil. Faraday had created an electric current by moving a magnet inside a copper coil. Still today, the essential parts of a hydroelectric generator are coiled wire and a moving electromagnetic field.
Generators consist of a fixed outer part called the stator and a moving inner part, the rotor, that is attached to the turbine's shaft. As mentioned previously, the turbine shaft turns the rotor within the generator. Electromagnets cover the rotor's outer surface, and the stator's inner surface consists of copper windings. As the rotor moves the electromagnets past the copper windings, the electrons in the copper vibrate to produce alternating electric current. The frequency of the alternating current, expressed in cycles per second, or Hertz, is determined by the number of times per second that the rotor magnets move past the stator's copper windings. The electricity goes from the generator into transformers that raise the voltage so the electricity can travel for long distances through power lines. Before it goes to end users, electricity again goes through transformers at substations to reduce the voltage. Then it goes through more power lines and through pole transformers to homes and businesses.