In 1878, Thomas A. Edison began work on the electric light and formulated the concept of a centrally located power station with distributed lighting serving a surrounding area. He perfected his light by October 1879, and the opening of his historic Pearl Street Station in New York city on September 4, 1882, marked the beginning of the electric utility industry. At Pearl Street, dc generators, then called dynamos, were driven by steam engines to supply an initial load of 30kW for 110-V incandescent lighting to 59 customers in a 1-square-mile area. From this beginning in 1882 through 1972, the electric utility industry grew at a remarkable pace – a growth based on continuous reductions in the price of electricity due primarily to technological accomplishment and creative engineering.
The introduction of the practical dc motor by Sprague electric, as well as the growth of incandescent lighting, promoted the expansion of Edison’s dc systems. The development of three-wire 220-V dc systems allowed load to increase somewhat, but as transmission distances and loads continued to increase, voltage problems were encountered. These limitations of maximum distance and load were overcome in 1885 by William Stanley’s development of a commercially practical transformer. Stanley installed an ac distribution system in Great Barrington, Massachusetts, to supply 150 lamps. With the transformer, the ability to transmit power at high voltage with corresponding lower current and lower line-voltage drops made ac more attractive than dc. The first single-phase ac line in the United States operated in 1889 in Oregon, between Oregon city and Portland – 21 km at 4 kV.
由Sprague电力引进的实用的直流电机及白炽灯的发展推动了爱迪生的直流系统的发展。3线220V直流系统的发明在一定程度上提高了供电负荷，但是当输电距离和负荷继续增加，电压成为一大问题。1885年William Stanley发明的经济可行的变压器解决了这一在输电距离和负荷上的限制问题。Stanley在Massachusetts的Great Barrington建立了一个交流配电系统，为150盏灯供电。变压器使得电能可以在更高电压和更低电流传输，降低了线路电压降，使交流系统比直流系统跟具吸引力。美国第一条单相交流线路1889年在Oregon运行，该线路21公里，电压等级为4kV，连接Oregon和Portland.
The growth of ac systems was further encouraged in 1888 when Nikola Tesla presented a paper at a meeting of the American Institute of Electrical Engineers describing two-phase induction and synchronous motors, which made evident the advantages of polyphase versus single-phase systems. The first three-phase line in Germany became operational in 1891, transmitting power 179 km at 12 kV. The first three-phase line in the United States (in California) became operational in 1893, transmitting power 12 km at 2.3 kV. The three-phase induction motor conceived by Tesla went on to become the workhorse of the industry.
In the same year that Edison’s steam-driven generators were inaugurated, a waterwheel-driven generator was installed in Appleton, Wisconsin. Since then, most electric energy has been generated in steam-powered and in water-powered (called hydro) turbine plants. Today, steam turbines account for more than 85% of U.S. electric energy generation, whereas hydro turbine account for about 7%. Gas turbines are used in some cases to meet peak loads.
Steam plants are fueled primarily by coal, gas, oil, and uranium. Of these, coal is the most widely used fuel in the United States due to its abundance in the country. Although many of these coal-fueled power plants were converted to oil during the early 1970s, that trend has been reversed back to coal since the 1973/74 oil embargo, which caused an oil shortage and created a national desire to reduce dependency on foreign oil. In 1957, nuclear units with 90MW steam-turbine capacity, fueled by uranium, were installed, and today nuclear units with 1312 MW steam-turbine capacity ware in service. However, the growth of nuclear capacity in the United States has been halted by rising construction costs, licensing delays, and public opinion.
Starting in the 1990s, the choice of fuel for new power plants in the United States has been natural gas. The gas-fired turbine is safe, clean, more efficient than competing technologies, and uncontroversial. As of 2001, the tread toward natural gas has accelerated. It is estimated that 200 large gas-fired plants are being developed, accounting for 75-90% of planned U.S. Expansion. However, increasing natural gas prices may slow this trend.
Other types of electric power generation are also being used, including wind-turbine generators; geothermal power plants, wherein energy in the form of steam or hot water is extracted from the earth’s upper crust; solar cell arrays; and tidal power plants. These sources of energy cannot be ignored, but they are not expected to supply a large percentage of the world’s future energy needs. On the other hand, nuclear fusion energy just may. Substantial research efforts have shown nuclear fusion energy to be a promising technology for producing safe, pollution-free, and economical electric energy later in the 21st century and beyond. The fuel consumed in a nuclear fusion reaction in deuterium, of which a virtually inexhaustible supply is present in seawater.
The early ac systems operated at various frequencies including 25, 50, 60, and 133 Hz. In 1891, it was proposed that 60 Hz be the standard frequency in the United States. In 1893, 25-Hz systems were introduced with the synchronous converter. However, these systems were used primarily for railroad electrification (and many are now retired) because they had the disadvantage of causing incandescent lights to flicker. In California, the Los Angeles Department of Power and Water operated at 50 Hz, but converted to 60 Hz when power from the Hoover Dam became operational in 1937. In 1949, Southern California Edison also converted from 50 to 60 Hz. Today, the two standard frequencies for generation, transmission, and distribution of electric power in the world are 60 Hz (in the United States, Canada, Japan, Brazil) and 50 Hz ( in Europe, the former Soviet republics, South America except Brazil, India, also Japan). The advantage of 60-Hz systems is that generators, motors, and transformers in these systems are generally smaller than 50-hz equipment with the same ratings. The advantage of 50-Hz systems is that transmission lines and transformers have smaller reactances at 50 Hz than at 60 Hz.
最早的交流系统以25Hz, 50Hz, 60Hz 和 133Hz各种频率运行。1891年60Hz成为美国的标准频率。1893年，通过采用同步换流器，开始使用25Hz系统。但是，这些系统主要用于铁路电气化(很多现在已经退役)，因为它们有造成白炽灯闪烁的缺点。加利福尼亚的水利电力部采用50Hz，但是，当1937年Hoover大坝开始运作，频率就转换为60Hz。1949年南加利福尼亚的Edison公司也将频率从50Hz转变为60Hz。今天，60Hz(在美国，加拿大，日本和巴西使用)和50Hz(在欧洲，前苏联，除巴西以外的南美洲，印度以及日本使用)是世界上发电，输电和配电的两个标准频率。60Hz系统的优点在于系统中的发电机，电动机和变压器通常比同等级50Hz系统的设备小。50Hz系统的优点是传输线和变压器的电抗在50Hz时较60Hz时小。
As shown in Figure 1.2, the rate of growth of electric energy in the United States was approximately 7% per year from 1902 to 1972. This corresponds to a doubling of electric energy consumption every 10 years over the 70-year period. In other words, every 10 years the industry installed a new electric system equal in energy-producing capacity to the total of what it had built since the industry began. The annual growth rate slowed after the oil embargo of 1973/74. Kilowatt-hour consumption in the United States increased by 3.4% per year from 1972 to 1980, and by 2.1% per year from 1980 to 2000.
Along with increases in load growth, there have been continuing in creases in the size of generating units. The principal incentive to build larger units has been economy of scale – that is, a reduction in installed cost per kilowatt of capacity for larger units. However, there have also been steady improvements in generation efficiency. For example, in 1934 the average heat rate for steam generation in the U.S. electric industry was 17,950 BTU/kWh, which corresponds to 19% efficiency. By 1991, the average heat rate was 10,367 BTU/kWh, which corresponds to 33% efficiency. These improvements in thermal efficiency due to increases in unit size and in steam temperature and pressure, as well as to the use of steam reheat, have resulted in savings in fuel costs and overall operating costs.
There have been continuing increases, too, in transmission voltages. From Edison’s 220-V three-wire dc grid to 4-kV single-phase and 2.3-kV three-phase transmission, ac transmission voltages in the United States have risen progressively to 150, 230, 345, 500, and now 765 kV. And ultra-high voltages (UHV) above 1000 kV are now being studied. The incentives for increasing transmission voltages have been: (1) increases in transmission distance and transmission capacity, (2) smaller line-voltage drops, (3) reduced line losses, (4) reduced right-of-way requirements per MW transfer, and (5) lower capital and operating costs of transmission. Today, one 765-kV three-phase line can transmit thousands of mega watts over hundreds of kilometers.