Alternating current

Alternating current
Zureks · Public domain · source
Name	Alternating current
Invented	19th century
Inventor	Multiple pioneers
Application	Power distribution, electronics, motors

Alternating current is an electrical current that reverses direction periodically and varies in magnitude over time, widely used for power distribution and alternating-voltage systems. It underpins modern Edison-era debates, influenced developments by Nikola Tesla, George Westinghouse, and shaped infrastructures in United States, United Kingdom, Germany, France, and Italy. The adoption of alternating systems transformed industrial revolutions in cities like New York City, Chicago, London, and Berlin and affected policies in institutions such as the U.S. Congress, British Parliament, and the German Empire.

History

Development of alternating systems involved inventors and companies including Michael Faraday, Heinrich Hertz, Nikola Tesla, George Westinghouse, Sir William Siemens, and firms like Westinghouse Electric Corporation, General Electric, and Siemens AG. Early demonstrations in the 19th century connected to research at Royal Institution and laboratories of University of Cambridge, University of Berlin, and Prussian Academy of Sciences. The so-called "war of currents" featured public disputes involving Thomas Edison, George Westinghouse, and legal and regulatory attention from bodies including the U.S. Patent Office and municipal authorities in Philadelphia and Boston. Large-scale deployments for events like the World's Columbian Exposition showcased alternating systems alongside advances by Westinghouse Electric and influenced policies in the American Institute of Electrical Engineers.

Theory and characteristics

Alternating waveforms are analyzed using mathematical frameworks developed by figures like Joseph Fourier, Carl Friedrich Gauss, Leonhard Euler, James Clerk Maxwell, and tools from institutions such as the Royal Society, Académie des Sciences, and Prussian Academy of Sciences. Key parameters—frequency, amplitude, phase—are described with standards set by organizations including the International Electrotechnical Commission, Institute of Electrical and Electronics Engineers, and national bodies like British Standards Institution and ANSI. Phenomena like impedance, reactance, resonance, and power factor connect to work by Oliver Heaviside, Heinrich Hertz, Maxwell, and theoretical frameworks used at Massachusetts Institute of Technology, École Polytechnique, and Technische Universität Berlin.

Generation and transmission

Generation technologies trace to turbo-generators and alternators developed by engineers at General Electric, Siemens AG, Alstom, and research centers such as Bell Labs and Imperial College London. Large-scale electrification projects in regions like Great Plains (United States), Rhine-Ruhr, and Nord-Pas-de-Calais relied on high-voltage AC transmission lines designed following work by Charles Proteus Steinmetz, Frank Sprague, and corporations such as Westinghouse Electric and General Electric Company (UK). Interconnection projects—exemplified by grids in United States, France, Germany, and across the European Union—involved regulators like Federal Energy Regulatory Commission and operators such as National Grid (UK), Électricité de France, and Réseau de Transport d'Électricité. Technologies for long-distance AC transmission include transformers invented by contributors from Imperial College-linked research and the transformer patents contested in courts like the U.S. Supreme Court.

Applications

Alternating current powers appliances, industrial motors, and transport systems developed by companies including General Electric, Siemens AG, Mitsubishi Electric, and Hitachi. Urban transit networks such as those in New York City Subway, London Underground, and Tokyo Metro utilize AC-driven systems and rail electrification standards set by bodies like International Electrotechnical Commission and Union Internationale des Chemins de fer. In manufacturing, induction motors trace to theories from Nikola Tesla and practical machines by Westinghouse; consumer electronics from firms like Sony, Samsung, and Panasonic adapt AC via power supplies designed following specs from IEEE and IEC.

Measurement and instrumentation

Instrumentation for AC measurement evolved in laboratories at Bell Labs, General Electric Research Laboratory, and universities including Massachusetts Institute of Technology and Stanford University. Devices such as oscilloscopes, wattmeters, and ammeters were refined by companies like Tektronix, Fluke Corporation, and standards committees at Institute of Electrical and Electronics Engineers and International Electrotechnical Commission. Calibration and metrology trace to national institutes such as National Institute of Standards and Technology, Physikalisch-Technische Bundesanstalt, and National Physical Laboratory (United Kingdom), which maintain traceability for frequency, voltage, and power measurements used in grids operated by PJM Interconnection and California ISO.

Safety and standards

Safety practices and regulatory frameworks derive from codes and standards published by International Electrotechnical Commission, Institute of Electrical and Electronics Engineers, Underwriters Laboratories, and national regulators like Occupational Safety and Health Administration and Health and Safety Executive (United Kingdom). Historical incidents prompted legislation and standards development involving investigations by agencies such as National Transportation Safety Board and courts like the U.S. Court of Appeals. Electrical installation rules, protective devices, grounding practices, and workplace regulations reference guidance from National Fire Protection Association (NFPA), British Standards Institution, and international agreements coordinated through the International Organization for Standardization.

Category:Electric power