The effects of an electric current are thermal, luminous, chemical and magnetic. When a current flows through a conductor it may heat the conductor. This heat is sometimes undesirable and has to be reduced. For this reason, many electric motors and generators contain a fan. However, domestic appliances, such as electric cookers, and many industrial processes depend on the heating effect of an electric current.
The passage of a current may produce light. This can happen in a number of ways. The heat generated by the current may be so great that the conductor becomes incandescent. Foe example, the filament of a light bulb emits intense white light when heated by a current. Light is also produced when a current ionizes a gas. The colour of the light will vary according to the gas used. Mercury vapour lamps give a greenish blue light.
An electric current can separate a chemical compound into its components. This is called electrolysis. Chlorine is generated by the electrolysis of saltwater. Electrolysis can also be used to break down water into hydrogen and oxygen. Because pure water doe not conduct well, sulphuric acid has to be added before the electrolysis takes place.
A current flowing through a conductor creates a magnetic field around it. This field has three applications. It can magnetize magnetic materials and attract them to the conductor. The electric relay works on this principle. If the magnetic field is cut by another conductor, an electromotive force will be induced in that conductor. For instance, the change in current flowing through the primary of a transformer will induce a current in the secondary. This principle is also used in generators. Thirdly, if a current carrying conductor is placed in the magnetic field, a force will be exerted on it. This effect is utilized in the electric motor.
incandescent – раскаленный;
chlorine – хлор;
sulphuric acid – серная кислота;
The production of electrical energy
21.
The production of electrical energy is, of course, basic in all power systems. Also, the operation of a power system almost always involves the transfer of electrical energy from one location to another. Except for generation facilities located at some industrial plants for their own use, and some small plants at locations such as apartment complexes, electrical power is normally produced at power plants operated by power utility systems or by other power producers who sell their power output to power users.
In most cases electrical power is produced by a generator which converts one form of energy (heat, moving water, or air) to electrical energy. Typically generators are driven by prime movers such as water or steam turbines. There are exceptions where electrical energy is produced by chemical reactions or by direct conversion of heat or light. These methods will be discussed later.
The production of electrical power is, of course, a fundamental requirement in the operation of power systems. There are several basic methods of producing electrical energy, such as mechanical, chemical, direct conversion and these may have variations.
Mechanical production of electrical energy. The most widely used method by far is by the conversion of mechanical into electric energy. The production of electrical energy by mechanical means always requires a prime mover to drive a generator. Prime movers are used to convert some energy source to mechanical movement. Such energy sources can be falling water, heat, wind. In the simplest case only one prime mover, one generator, and a load are involved.
Notable exceptions are direct conversion processes where other forms of energy are directly converted into electric energy. These processes include photoelectric, which directly converts solar or light energy$ thermoelectric, which directly converts heat energy into electric energy, and chemical, which converts chemical energy into electric energy (batteries).
power utility systems – энергосистемы общего пользования;
power output – отдаваемая (выходная) мощность;
ПРИЛОЖЕНИЕ 1
