Communication of power throughout the world

Electricity is one of if not the most important sources of energy in the world. Today almost every household and business in the United States is run primarily on electricity. This constitutes a large number customers spread out over a very large area.

The power venders of the world operate over a very complex web of generation plants, transmission lines, substations, and terminations. As you might guess, operation of this web is a very complex job. It would be similiar to that of the phone company's long distance lines. Operations must be kept in order that power is kept at a steady rate to all people at all times. This means that lines must be kept in order and tracked to where alternate lines can be used should one fail. Alternate plants must be seeked should one loss power. Plant output must be watched to be sure that a plant can handle the load that is being placed upon it.

Early Beginnings

The electric power industry of the United States grew from small beginnings such as these to become, in less than 100 years, the most heavily capitalized industry in the country. It now comprises about 3,100 different corporate entities, including systems of private investors, federal and other government bodies, and cooperative-user groups. Less than one-third of the corporate groups have their own generating facilities; the others are directly involved only in the transmission and distribution of electric power.

STANDARD ELECTRIC GENERATING PLANTS

Virtually all commercial electric energy is now produced by generators driven by steam from the burning of fossil fuels or from nuclear sources or by hydropower. Developed nations depend mainly on fossil fuels, but some countries now depend more heavily on NUCLEAR ENERGY produced by materials such as uranium. France, for example, generates about 70% of its electricity from nuclear power plants; power costs in that nation are the lowest in Europe.

A basic steam-power plant includes a furnace or reactor for raising the temperature of the water in a boiler, or steam generator, until it changes into steam, and a turbine, which drives the generator to produce electric power. Throughout the history of the electric power industry, improvements in design, metallurgy, fabrication techniques, and control systems have permitted continual increases in the size, operating temperatures, pressures, and efficiencies of electric generating units. These improvements and increasing demands for electric power have led generating facilities to develop from the early steam-engine-driven generator, which could produce a few kilowatts (kW), today's giants, with outputs as high as 1,300,000 kW. Hydroelectric, or waterpower, generators have grown from the 12-kW machines of 1882 to the 600,000-kW units at the Grand Coulee station in Washington state (see HYDROELECTRIC POWER).

All electric-utility systems experience cyclic load patterns involving higher demands for electric power at some hours of the day and some seasons of the year than at others. Such considerations affect the design of a utility's generating capacity plant because some types of generating equipment are better suited to supplying base, or continuous, loads and may not operate satisfactorily or economically over a varying load cycle; others are better designed for the variable loading, intermittent use, and frequent start-up and shutdown required by such patterns of operation. Hydroelectric plants are often well adapted to intermittent operation and may be useful for supplying peaking power. They can be constructed only in special locations, however, and they must often rely on fuel plants to supply peaking needs. Steam plants especially designed for peaking service have been installed in a few systems, and internal combustion units have sometimes been used for such service.

ELECTRIC POWER TRANSMISSION

Electric power transmission systems consist of step-up transformer stations to connect the lower-voltage power-generating equipment to the higher-voltage transmission facilities; high-voltage transmi ssion lines and cables for transferring power from one point to another and pooling generation resources; switching stations, which serve as junction points for different transmission circuits; and step-down transformer stations that connect the transmission circuits to lower-voltage distribution systems or other user facilities. In addition to the transformers, these transmission substations contain circuit breakers and associated connection devices to switch equipment into and out of service, lightning arresters to protect the equipment, and other appurtenances for particular applications of electricity. Highly developed control systems, including sensitive devices for rapid detection of abnormalities and quick disconnection of faulty equipment, are an essential part of every installation in order to provide protection and safety for both the electrical equipment and the public.

Overhead Transmission Lines

Many of the first high-voltage transmission lines in the United States were built principally to transmit electrical energy from hydroelectric plants to distant industrial locations and population centers. High-voltage transmission lines were originally designed to permit the construction of large generating units and central stations on attractive, remote sites close to fuel sources and supplies of cooling water. Today, however, they connect different power networks in order to achieve greater economy by exchanges of low-cost power, to achieve savings in reserve generating capacity, to improve the reliability of the system, and to take advantage of diversity in the peak loads of different systems and thereby reduce operating costs.

At one time power lines in the 33-kV or 44-kV class were classified as high-voltage lines. As loads increased and transmission distances became greater, transmission voltages were increased. Electrical losses increase proportionately to the square of the current--the higher the voltage of the line, the lower the current needed to carr y an equivalent amount of power. Moreover, one high-voltage line can usually carry as much power as several lower-voltage ones, so the use of higher voltages reduces the number of lines required and conserves the space required for rights-of-way. Voltage levels increased to 69, 115, 138, and 161 kV in various sections of the United States. Before World War II the highest-voltage lines in the United States were 230 kV, with the exception of one 287-kV line from Boulder Dam to Los Angeles. In the early 1950s several 345-kV lines were constructed. By 1964 the first 500-kV lines in the United States were being completed, and in 1969 the first 765-kV line was put into service. All of these involved AC systems.

In 1970 a 1,380-km (856-mi), 800-kV direct-current (DC) line was placed in commercial service to connect northwestern U.S. hydroelectric sources with the Los Angeles area. Such systems offer an economical means of transferring large quantities of power over long distances. They also avoid stability problems sometimes encountered by AC systems ; DC systems are sometimes used to connect AC systems even over short transmission distances.

Many transmission circuits utilize underground cables, although these installations have been limited largely to locations where rights-of-way for overhead lines could not be obtained or where overhead lines were not feasible because they would have interfered with other activities. In general the costs of underground circuits are several times those of comparable overhead circuits.

Insulation problems are very different with underground cables from those with overhead lines, in which air serves as a major insulating medium. A number of different types of cable designs and insulations have been used in the United States. Solid synthetic insulating materials have given satisfactory results in the lower voltage ranges, but for high-voltage applications the principal insulator is gas, or an, oil-paper combination. Some extruded synthetic insulations have recently been developed that use materials such as polyethylene.

One common kind of gas- and oil-insulated cable, known as self-contained cable, uses a conductor formed around a hollow core that is later filled with oil under low pressure. The conductor is insulated with an oil-impregnated paper, and the entire assembly is covered with a metal sheath. Three such cables are required, one for each phase of a three-phase power circuits normally used for alternating current transmission throughout the world. Another cable system, known as pipe-type, utilizes conductors insulated with oil-impregnated paper and covered with metallic and synthetic sheathing tapes. Three of these cables are pulled into a single pipe that is then filled with either gas or oil under high pressure. In the United States, the pipe-type system has been used most.