Power Supply
All power supplies provide electrical energy to do work, but how the feat has been accomplished over the centuries has varied considerably. The first power supplier was the Leyden jar. Invented in 1745, it could store sizeable electric charges created by electrostatic devices, such as Alessandro Volta's electrophorus. The charge could be drawn from the jar and put to work. In 1800, Volta created the first battery, the "Voltaic pile." This reliable source of power produced electricity by means of a chemical reaction.
The first mechanical electrical generator was invented by Michael Faraday in 1831. Joseph Henry and Faraday had independently discovered that a moving magnetic field could create the flow of electricity in a conductor. Faraday used this process of electrical induction to create an alternating current power supply. Soon after, Hippolyte Pixii built a hand-driven generator that produced alternating current (AC), and added a commutator to convert the power into direct current (DC).
In 1867, inventor Zénobe Gramme, using the principles established by Henry and Faraday, built an improved dynamo for producing AC, and two years later he improved the DC dynamo. The two methods of power production divided scientists, with factions led by Thomas Edison and Nikola Tesla. Edison's invention of the incandescent light bulb in 1879 had created a demand for electricity, so he established a DC-generated power supply company in New York City. Direct current power supplies had two main disadvantages: power production was limited by arcing from the brushes that drew electricity from the dynamo's rotor, and long-distance transmission was prevented by resistance in electrical wires carrying the current. In 1884 Edison's plant was supplying power to over 11,000 electric lights in 500 buildings, with another 60,000 buildings receiving power from individual generators Edison had supplied.
Tesla, who had worked with Edison, tried to convince him that AC was the wave of the future. It could be produced in abundance without arcing, and could be carried very efficiently over power lines. Unable to persuade Edison, Tesla took his ideas to George Westinghouse. In 1893, Tesla and Westinghouse successfully used AC power supplies to provide electricity for the World Columbia Exposition in Chicago, ending the monopoly of DC dynamos. In 1895 the first hydroelectric AC power generator began operation at Niagara Falls and, with the use of power transformers, supplied electricity over great distances.
Alternating current power is created by rotating conductors (turbines) within a magnetic field. Water is heated (by burning wood or coal, or through atomic decay) and steam pressure is produced, rotating the turbines. In hydroelectric plant, the force of moving water is used to spin turbines. Gas turbines and tidal power are also used. The standard AC power systems in use today are either three-phase with three wires, mainly for use in transmission of high voltages, or three-phase with four wires, where low voltage power is needed. They operate at a frequency of either 50 or 60 Hertz (cycles per second), with each phase synchronized to the entire system. Voltage going into a system can be controlled by changing the "tapping" on transformers to alter voltage ratios, varying the rotor field strength, or switching in and out shunt reactors. The frequency of the system is controlled by adjusting the steam supply going to the turbines. Power is created at remotely located generating stations, stepped up by transformers, and distributed to substations where step-down transformers, switches (busbars), isolaters and circuit breakers are used to reduce the voltage and protect equipment.
The transformed power is sent out over various distribution networks which handle the appropriate voltage to supply the demand. Duplication of power supplies, transformers and distribution networks back up the system in case of a failure. Power is transmitted over long distances by underground cables or overhead lines, each with its advantages. Underground cables are free from the danger of storms and falling trees, but difficult to access when problems arise. Above-ground lines are cheaper to install, but vulnerable and unsightly. Some have claimed that high electric and magnetic fields produced by high-tension wires could be a health risk to people living in their vicinity, but most studies now seem to refute this idea, except for the possibility of some childhood leukemias from high-current power lines.
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