![]() The technique can also be extended to higher order phase systems. ![]() Essentially, this method converts three unbalanced phases into three independent sources, which makes asymmetric fault analysis more tractable.īy expanding a one-line diagram to show the positive sequence, negative sequence, and zero sequence impedances of generators, transformers and other devices including overhead lines and cables, analysis of such unbalanced conditions as a single line to ground short-circuit fault is greatly simplified. In a three-phase system, one set of phasors has the same phase sequence as the system under study (positive sequence say ABC), the second set has the reverse phase sequence (negative sequence ACB), and in the third set the phasors A, B and C are in phase with each other (zero sequence, the common-mode signal). In 1943 Edith Clarke published a textbook giving a method of use of symmetrical components for three-phase systems that greatly simplified calculations over the original Fortescue paper. Only a single frequency component is represented by the phasors. In 1918 Charles Legeyt Fortescue presented a paper which demonstrated that any set of N unbalanced phasors (that is, any such polyphase signal) could be expressed as the sum of N symmetrical sets of balanced phasors, for values of N that are prime. Set of three unbalanced phasors, and the necessary symmetrical components that sum up to the resulting plot at the bottom.
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