Symmetrical components
From Biocrawler, the free encyclopedia.
In electrical engineering, the method of Symmetrical components is used to simplify analysis of unbalanced three phase power systems.
Charles L. Fortescue in a paper presented in 1918 (Method of Symmetrical Co-Ordinates Applied to the Solution of Polyphase Networks) demonstrated that any set of unbalanced three-phase quantities could be expressed as the sum of three symmetrical sets of balanced phasors.
One set of phasors had the same phase sequence as the system under study (positive sequence), the second set had the reverse phase rotation (negative sequence), and the third set did not rotate (zero sequence). By expanding a one-line diagram to show the positive sequence, negative sequence and zero sequence impedances of generators and transformers and other devices, analysis of such unbalanced conditions as a single line to ground short-circuit fault is greatly simplified. The technique can also be extended to higher phase order systems. Only a single frequency component is represented by the phasors.
The analytical technique was adopted and advanced by engineers at General Electric and Westinghouse and after World War II it was an accepted method for asymmetric fault analysis.
Charles LeGeyt Fortescue was born in 1876 in York Factory, in what is now Manitoba where the Hayes River enters Hudson Bay. He was the son of a Hudson's Bay Company fur trading factor and was among the the first graduates of the Queen's University electrical engineering program in 1898. He spent most of his professional career working for Westinghouse and died in 1936. A fellowship awarded every year by the IEEE in his name commemorates his contributions to electrical engineering.
References
William D. Stevenson, Jr. Elements of Power System Analysis Third Edition, McGraw-Hill, New York (1975) ISBN 0070612854
History article from IEEE on early development of symmetrical components, retrieved May 12, 2005 (http://www.ieee.org/organizations/pes/public/2004/nov/peshistory.html)
