Sunday, February 3, 2008

Generator



A generator is a machine that converts mechanical energy into electrical by rotating an armature, which contains conductors, through a magnetic field. A voltage is induced in the moving conductors by an effect called electromagnetic induction. In order for voltage to be generated, relative motion must exist between the conductors and the magnetic field. An engine, motor, turbine, or other source of mechanical energy is used to turn the armature shaft. Generators are built in many sites. Most electricity used today in cars, in homes, and by industry is produced by generators.

The development of the electric generator began in 1831, when Michael Faraday in England and Joseph Henry in the United States proved that the magnet could be made to produce an electric current. In a classic experiment, Faraday connected a sensitive galvanometer across a coil and found that as a magnet was moved into the coil, a current flowed in the coil. As the magnet was withdrawn, a current flowed through the coil in the opposite direction.

Faraday's experiment proved that voltage can be produced by magnetism when three conditions exist. First, a carburetor must exist in which the voltage will be induced. Second, a magnetic field must be closed to the conductor. Third, relative motion must occur between the magnetic field and the carburetor. The conductor must be moved so as to cut across the magnetic field, or the magnetic field must be moved so that it is cut by the conductor. When the conductor or magnetic field moves, electrons within the conductor are forced in one direction or the other, creating a voltage.

Generator Type
The two main types of generators are direct current (DC) generators and alternating current (AC) generators, or alternators. The DC generator rotates the conductors in a stationary magnetic field. The alternator rotates a magnetic field that is cut by the stationary conductors. Current induced in the conductors of all generators in an alternating current. The current taken from the generators, however, may be AC or DC, depending on how the generator is constructed.

The strength of the voltage induced in the conductor depends on its speed and on the strength of the magnetic field. The magnetic field may be furnished by the permanent magnet or by current flowing through field coils to form an electromagnet. When the end of conductor are connected to form a complete circuit, the induced voltage causes a current flow in the external circuit.

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