Andy McDonald age 14, of St. Paul, Minn., for his question:
HOW DOES AN ELECTRIC GENERATOR WORK?
In 1831 an English physicist named Michael Faraday discovered that electricity could be produced in a coil of copper wire by moving the coil near a magnet or by moving a magnet near the coil. Today's electric generators produce electricity by means of this same principle. The process is called electromagnetic induction.
An electric generator is a piece of equipment used to produce electricity. Almost all electricity used by man today comes from generators.
Two types of generators mainly are used today: direct¬current generators, which produce electric current that always flows in the same direction; and alternating current generators which are also called alternators which produce electric current that reverses direction many times every second. Both types work on the same scientific principles, but they differ in the ways they are built and used.
Electric generators were once called dynamos, a shortened term for dynamoelectric, but today they are known as electric generators, or simply generators.
A generator does not create energy but changes mechanical energy into electrical energy. The generator must be driven by a turbine or some other machine that produces mechanical energy. It has two main parts: an armature and a field structure. The armature has coils of wire in which the electricity is induced. The field structure sets up the magnetic lines of force.
Electricity can be generated either by making the armature cut the lines of force, or by making the lines of force cut past the armature. Because of this, either the armature or the field structure can be the rotating part of a generator. The rotating part is called the rotor, and the stationary part is known as the stator.
A generator can be small enough to hold in your hand. It can also be larger than a house. Its output is usually measured in kilowatts. One kilowatt equals 1,000 watts, which is the power needed to light 10 100 watt light bulbs. A giant generator often produces more than 1 million kilowatts of electricity.
In almost all electric power plants you'll find alternating current generators. Direct current generators are found in locomotives and ships that are driven by diesel electric motors.
A simple electromagnetic device called a transformer makes it easy to increase or decrease the voltage of alternating current. Engineers build alternating current generators that produce current with voltage of 18,000 or 22,000 volts. By means of a step up transformer, the voltage can be increased as high as 230,000 or 345,000 volts to force the current over long distances. In the area where the current is finally used, a series of step down transformers can lower the voltage to a usable level. Most homes, for example, operate on 115 volts.