Alternating Current (AC) Generators
A magnet creates magnetic lines of force on either side of it that move in opposite directions. As the metal coil passes through the magnetic fieldin a generator, the electrical power that is produced constantly changes. At first, the generated electric current moves in one direction (as from left to right). Then, when the coil reaches a position where it is parallel to the magnetic lines of force, no current at all is produced. As the coil continues to rotate, it cuts through magnetic lines of force in the opposite direction, and the electrical current generated travels in the opposite direction (as from right to left). The ends of the coil are attached to metal slip rings that collect the electrical current. Each slip ring, in turn, is attached to a metal brush, which transfers the current to an external circuit.Thus, a spinning coil in a fixed magnetic field will produce an alternating current, one that travels first in one direction and then in the opposite. The rate at which the current switches back and forth is known as its frequency. Ordinary household current alternates at a frequency of 60 times per second (or 60 hertz).The efficiency of an AC generator can be increased by substituting an armature for the wire coil. An armature consists of a cylinder-shaped iron core with a long piece of wire wrapped around it. The longer the piece of wire, the greater the electrical current that can be generated by the armature.Commercial generators. One of the most important uses of generators is the production of large amounts of electrical energy for use in industry and homes. The two most common energy sources used in operating AC generators are water and steam. Both of these energy sources have the ability to drive generators at the very high speeds at which they operate most efficiently, usually no less than 1,500 revolutions per minute.In order to generate hydroelectric (water) power, a turbine is needed. A turbine consists of a large central shaft on which are mounted a series of fanlike vanes. As moving water strikes the vanes, it causes the central shaft to rotate. If the central shaft is then attached to a very large magnet, it causes the magnet to rotate around a central armature, generating electricity.Steam power is commonly used to run electrical generating plants. oil, or natural gas is burned or the energy from a nuclear reactor is harnessed to boil water to create steam. The steam is then used to drive a turbine which, in turn, spins a generator.
