Electric power is the use of electric energy to do work. It lights, heats, and cools many homes. Electric power also runs television sets, refrigerators, vacuum cleaners, and many other home appliances. Electric power operates machinery in factories. Escalators, elevators, and computers and other business machines in stores and offices use electric power. Electric power drives many trains and subway systems. On farms, electric machinery performs such tasks as pumping water, milking cows, and drying hay.
Huge electric generators in power plants produce almost all the world’s electric power. The majority of these plants burn coal, oil, or natural gas to run the generators. Most other plants drive the generators by means of nuclear energy or the force of falling water. Wires carry the electric current from power plants to the cities or other areas where it is needed. The electric power is then distributed to individual consumers.
Electric power is measured in units called watts. For example, it takes 100 watts of electric power to operate a 100-watt light bulb. Ten 100-watt bulbs require 1,000 watts, or 1 kilowatt. The amount of energy used is expressed in kilowatt-hours. A kilowatt-hour equals the amount of work done by 1 kilowatt in one hour. If you burn ten 100-watt bulbs for one hour or one 100-watt bulb for 10 hours, you use 1 kilowatt-hour of electric energy.
The world’s electric power plants can produce over 8 billion kilowatts of electric power at any given time. China leads all other countries in generating capacity. Chinese power plants can generate more than 2 billion kilowatts. American plants can generate more than 1 billion kilowatts.
Sources of electric power
Large electric power plants supply nearly all the electric power that people use. The power plants first harness the energy of steam or flowing water to turn the shaft of a device called a turbine. The turning shaft drives an electric generator, which converts the shaft’s mechanical power into electric power.
An electric generator has a stationary part called a stator and a rotating part called a rotor. In the huge electric generators used in power plants, the stator consists of hundreds of windings of wire. The rotor is a large electromagnet that receives electric power from a small separate generator called an exciter. An external source of mechanical energy, such as a turbine, turns the rotor. The turning of the rotor creates a magnetic field that turns along with the rotor. As this field rotates, it produces a voltage in the wire windings of the stator that causes a flow of electric current. See Electric generator.
The major types of electric power plants are (1) fossil-fueled steam electric power plants, (2) hydroelectric power plants, and (3) nuclear power plants. Various other kinds of power plants produce smaller amounts of electric power.
Fossil-fueled steam electric power plants
generate about three-fifths of both the world’s electric power and the electric power produced in the United States. Such plants burn coal, oil, or natural gas. These substances are called fossil fuels because they developed from the remains of prehistoric plants and animals. The fuel is burned in a combustion chamber to produce heat. The heat, in turn, is used to convert water in a boiler to steam. The steam then flows through a set of tubes in a device called a superheater. Hot combustion gases surround the steam-filled tubes in the superheater, increasing the temperature and pressure of the steam in the tubes.
The superheated, high-pressure steam is used to drive a huge steam turbine. A steam turbine has a series of wheels, each with many fanlike blades, mounted on a shaft. As the steam rushes through the turbine, it pushes against the blades, causing both the wheels and the turbine shaft to spin. The spinning shaft turns the rotor of the electric generator, thereby producing electric power. See Turbine (Steam turbines).
After the steam has passed through the turbine, it enters a condenser. In the condenser, the steam passes around pipes carrying cool water. The water in the pipes absorbs heat from the steam. As the steam cools, it condenses into water. This water is then pumped back to the boiler to be turned into steam again.
At many power plants, the water in the condenser pipes, which has absorbed heat from the steam, is pumped to a spray pond or a cooling tower to be cooled. At a spray pond, the water is sent through nozzles that form a spray of droplets. The spray increases the surface area of the water that is exposed to the air, quickly cooling the water. A cooling tower has a series of decks. The water spills down from one deck to another, cooling as it comes into contact with the air. The cooled water is recycled through the condenser or discharged into a lake, river, or other body of water.
Fossil-fueled steam electric power plants are efficient and reliable. But they can cause pollution. Some power plants do not use cooling towers or spray ponds. They release heated water into lakes, ponds, rivers, or streams. Such thermal pollution may harm plant and animal life in these bodies of water. In many areas, laws limit the discharge of heated water by power plants.
The smoke from burning fossil fuels causes air pollution and contributes to global warming if it is released into the atmosphere. Most power plants that burn these fuels use pollution control equipment to limit the release of pollutants. However, the use of such equipment has not fully eliminated the air pollution created by plants that burn fossil fuels.
Hydroelectric power plants
generate over 15 percent of the world’s electric power and about 7 percent of the electric power produced in the United States. Such plants convert the energy of falling water into electric energy. A hydroelectric plant uses water that is stored in a reservoir behind a dam. The water flows through a tunnel or pipe to the plant’s water turbine, or hydraulic turbine. As the water rushes through the turbine, it spins the turbine shaft, which drives the electric generator. See Water power; Turbine (Water turbines).
Hydroelectric power plants called pumped-storage hydroelectric plants can store energy by operating in reverse. When the demand for electric power is low, such plants can use their generators as motors to turn the turbines. The turbines then function as pumps, raising water to the reservoir. The water can be used at a later time to produce electric power.
Hydroelectric power plants cost less to operate than fossil-fueled plants and do not pollute the air. The number of hydroelectric power plants is limited, however, by the availability of water power and suitable locations for dams and reservoirs.
Nuclear power plants
generate about 10 percent of the world’s electric power and about 20 percent of the electric power generated in the United States. Nuclear plants produce electric power in much the same way that fossil-fueled plants do. But instead of a fuel-burning combustion chamber, a nuclear power plant has a device called a nuclear reactor. A nuclear reactor produces enormous amounts of heat by fissioning (splitting) the nuclei of atoms of a heavy element. Most nuclear plants use the element uranium as the fuel in their reactors.
Heat from the nuclear fission is used to convert water into steam. The steam drives the steam turbine that runs the electric generator. After the steam has left the turbine, it is condensed and recycled through the plant. Many nuclear power plants use cooling towers to cool the water from the condenser pipes.
A nuclear power plant requires much less fuel than a fossil-fueled plant to produce an equal amount of electric power. Nuclear plants also cause much less air pollution. However, they contain dangerous radioactive materials. As a result, the plants must install special safety systems to help prevent and quickly deal with accidents that could cause the release of radiation. Nuclear power plants cost more to build than fossil-fueled plants, partly because of the expense of the safety systems. Nuclear plants also create radioactive wastes that remain hazardous for thousands of years and therefore must be disposed of with extreme caution. See Nuclear energy.
Other sources of electric power
produce relatively small amounts of electric power. Wind energy is the most important and fastest growing of such power sources. Wind turbines use aerodynamic blades and a rotor to harvest wind energy and drive electric generators. Geothermal power plants use steam from the depths of the earth to run turbines that drive electric generators. Some power plants use the energy of the ocean tides to turn turbines that run generators. Others burn wood or agricultural wastes to drive generators. A few power plants convert the sun’s energy into electric power by means of devices called solar cells. Producing electric power with solar cells is expensive. However, scientists and engineers are studying ways to improve solar cells in order to produce large quantities of electric power more economically. See Solar energy.
Wind turbines generating power
A number of electric power plants have gas turbines or diesel engines to drive auxiliary generators. Such generators supply the extra power needed in times of high demand. Diesel engines are also used to drive generators in isolated areas not served by power companies. Many hospitals, factories, and apartment buildings have diesel engines to drive generators in case the distribution of electric power from power plants is disrupted.
Transmitting and distributing electric power
The electric power generated by power plants is usually transmitted 50 miles (80 kilometers) or more to cities or other areas. From those areas, it is distributed to nearby houses, factories, farms, offices, and other consumers. An electric power distribution system is sometimes called a power grid.
Transmission.
Most electric power travels from power plants along overhead wires called transmission lines. Laying underground or underwater cables generally costs more than stringing overhead wires. Cables are therefore used much less often than overhead wires.
As electric current moves along transmission lines, the lines resist the current flow. The resistance causes the current to lose energy by heating the lines. Power plants limit energy losses by transmitting electric power at high voltages. As voltage is increased, the amount of current needed to transmit a particular amount of electric power decreases. Because less current flows through the line, there is less energy lost due to resistance.
Electric current may be either direct current (DC) or alternating current (AC). Direct current flows in only one direction. Alternating current reverses direction many times each second. It is easier to boost the voltage of alternating current than that of direct current. Alternating current is therefore easier to transmit than direct current. For this reason, electric power plants generate alternating current.
The typical power plant generator can produce about 1 million kilowatts of electric power at up to 22,000 volts. Devices called step-up transformers then boost this voltage as high as 765,000 volts for transmission.
Distribution.
Some large industries require high-voltage current and receive it directly from transmission lines. But high-voltages are unsafe in homes, offices, and most factories. The voltage must therefore be decreased before electric power is distributed to them.
High-voltage electric current is carried by the transmission lines to subtransmission substations near the area where the power will be used. These substations have devices called step-down transformers that reduce the voltage to 12,500 to 138,000 volts. The voltage is then further reduced at distribution substations to 2,000 to 34,500 volts. Distribution lines may carry this medium-voltage current directly to commercial, industrial, or institutional users. Distribution lines also carry electric power to distribution transformers on poles, on the ground, or in underground vaults. Distribution transformers reduce the voltage to the levels needed by most users. Wires from the transformers run to homes, stores, offices, and other users. Nearly all such consumers in the United States and Canada receive electric power at about 110 or 220 volts.
Providing reliable service.
Equipment failures or damage caused by storms or accidents can interrupt local service of electric power. Such interruptions are known as power blackouts. Engineers called load dispatchers keep track of the flow of current through the transmission network. When a blackout occurs, the load dispatcher may restore service to the affected area by rerouting current along usable lines.
The demand for electric power often varies greatly from hour to hour. For example, sudden, dark storm clouds will increase demand because many lights will be turned on. The load dispatcher forecasts changes in demand and adjusts the generation and transmission of power accordingly. When demand exceeds the generating capacity of a power plant, the load dispatcher may reduce the voltage to prevent a blackout. Such a situation, called a brownout, may damage electrical equipment or cause it to operate less efficiently.
The transmission networks of most electric companies are interconnected, forming a power pool. Power pools enable companies to receive power from one another in an emergency. Computers control the flow of electric current through transmission networks.
The electric power industry
Organizations called electric utilities generate, transmit, and distribute the majority of the electric power that the public uses. Electric utilities are either owned or regulated by government agencies. In some countries, the national government owns all electric utilities. In others, stockholders or cooperatives, or local or regional governments, may own electric utilities in addition to the national government. Usually, a geographical area is served by a single electric utility. In some countries, including the United States and Canada, electric power generation has been partially deregulated. In deregulated markets, a growing number of privately owned businesses called independent power producers generate electric power and supply it wholesale to utilities. The United States is one of the world’s leading generators and consumers of electric power.
Some countries can generate more electric power than they need, and they export this excess power. Canada exports electric power to the United States, France exports to the United Kingdom, and many African countries export to neighboring nations.
In the United States,
there are about 3,400 electric utilities, and about 1,700 power producers that are not utilities. Electric utilities account for a little over half of the nation’s generating capacity. The rest of the utilities do not generate power. They only transmit it, distribute it, or both. Utilities in the United States may be owned by stockholders, cities, cooperatives, public power districts, or state or federal government agencies. Public power districts are political subdivisions that provide electric power to both incorporated cities and towns and unincorporated rural areas. Nonutilities, including independent power producers, account for a little under half of the nation’s generating capacity.
Local and state utility commissions usually set the rates that electric utilities charge their customers. Federal agencies govern the design and licensing of power plants, regulate the interstate sale of electric power, and set and enforce pollution control standards.
In 1992, the U.S. government began to take steps to deregulate the electric power industry. Many states now have open competition among utilities and other power providers.
In Canada,
the governments of the various provinces own most major electric utilities. But stockholders own large electric utilities in Alberta and Prince Edward Island. Provincial public utility boards regulate Canada’s electric utilities. The federal Canadian Nuclear Safety Commission oversees the nuclear energy industry. The National Energy Board controls the export of electric power.
History
Early developments.
One of the earliest practical uses of electric power was to light the lamps of lighthouses. In 1858, South Foreland Lighthouse near Dover, England, became the first electric lighthouse. Its generator powered an arc lamp. An arc lamp produces bright light by means of an electric arc (see Electric arc). Beginning in the 1870’s, arc lamps illuminated such places as railroad stations, factories, and public squares in major cities in Europe and the United States.
In 1879, the California Electric Light Company in San Francisco began operating the world’s first central power plant that sold electric power to private customers. Also in 1879, the American inventor Thomas A. Edison perfected a lamp that gave off light when a filament inside it was heated by an electric current. Edison’s incandescent lamp burned much longer than an arc lamp. It quickly created a growing demand for electric service.
Loading the player...Thomas Alva Edison
Growth of the electric power industry.
By the end of the 1800’s, there were over 3,600 electric utilities in the United States. However, they did not all provide electric power at the same voltages. Studies conducted by electrical engineers in 1891 resulted in standardization of voltages. Utilities could then form power pools.
In the early 1930’s, only about 10 percent of U.S. farms had electric power. President Franklin D. Roosevelt established the Rural Electrification Administration (REA) in 1935 to expand electric service in rural areas. By the early 1990’s, nearly all U.S. farms had electric power.
The first full-scale nuclear power plant began operation in 1956 at Calder Hall in northwestern England. In 1966, the world’s first tidal power plant opened on the Rance River near St.-Malo, France.
Electric power today.
Electric utilities rely increasingly on computerized control systems. Power lines are widely interconnected among electric companies. Power companies must plan carefully for the addition of plants and transmission lines to meet the ever-increasing demand for electric power. The construction of new plants is costly and takes several years. Many planned nuclear power plants have been canceled because of soaring construction costs as well as safety concerns.
The supply of fossil fuels will eventually run out unless economical substitutes can be developed for them. Many scientists believe that energy from the earth, sun, wind, and oceans can be used more extensively to produce electric power in the future. Some utilities now use solar, geothermal, tidal, or wind energy in addition to regular energy sources to generate electric power.
In August 2003, North America experienced its worst power outage in history. The outage affected eight U.S. states in the Northeast and Midwest and two Canadian provinces. Investigators believe that it began in Ohio after a series of routine, and brief, transmission line shutdowns. It spread as power lines overloaded and circuit breakers triggered the shutdown of several lines and coal-fired plants. After detecting power fluctuations, several nuclear power plants automatically disconnected from the grid to prevent equipment damage. Many people have criticized the instability of the nation’s aging transmission system and have called for an upgrade of the transmission equipment.
