Alternating current

From Simple English Wikipedia, the free encyclopedia

City lights viewed in a motion blurred exposure. The AC blinking causes the lines to be dotted rather than continuous.

An alternating current (AC) is an electric current of which magnitude and direction vary. That is the difference to direct current, whose direction remains constant.

The usual waveform of an AC power circuit is a sine wave, because this leads to the most efficient transmission of energy. But in certain applications there are used different waveforms, such as triangular or square waves.

When one speaks of alternating current one mostly refers to the form in which electricity is delivered to businesses and residences. But audio and radio signals carried on electrical wire are also examples of alternating current. In these applications, an important goal is often the recovery of information encoded (or modulated) onto the AC signal.

1 History
2 Further reading
3 See also
4 External links

[edit] History

William Stanley, Jr. designed one of the first practical devices to transfer AC power efficiently between isolated circuits. Using pairs of coils wound on a common iron core, his design, called an induction coil, was an early precursor of the modern transformer. The system used today was devised in the late ninteenth century, largely by Nikola Tesla. Contributions were also made by George Westinghouse, Lucien Gaulard, John Dixon Gibbs,Wilhelm Siemens and Oliver Shallenger. AC systems overcame the limitations of the direct current system used by Thomas Edison to distribute electricity efficiently over long distances.

The first modern commercial power plant that used three-phase alternating current was at the Mill Creek hydroelectric plant near Redlands, California in 1893. Its designer was Almirian Decker, a brilliant young engineer. Decker's innovative design incorporated 10,000 volt three phase transmission and established the standards for the complete system of generation, transmission and motors used today.

[edit] Further reading

Willam A. Meyers, History and Reflections on the Way Things Were: Mill Creek Power Plant - Making History with AC, IEEE Power Engineering Review, February 1997, Pages 22-24