Improvements in and relating to three-phase symmetrical component analysers and their application in electrical protective relay systems

摘要

902,999. Protective cut-out arrangements. ENGLISH ELECTRIC CO. Ltd. Aug. 14, 1958 [March 11, 1958], No. 7788/58. Class 38 (5). A network for deriving signals representing the positive and negative phase-sequence current components of a protected circuit is energized from current transformers CT which are delta-connected so as to remove the zerosequence components. The network comprises 1 : 1 ratio auxiliary transformers A.C.T. which energize impedances Z 1 , Z 2 in accordance with one phase current iq. The other phase currents ip and ir energize impedances Z 1 L60‹ and Z 2 L60‹ such that the sum of the potential drops across the impedances Z 1 , Z 1 L60‹ is a measure of the negative phase-sequence components and the sum of the potential drops across the impedances Z 2 , Z 2 L60‹ is a measure of the positive phase-sequence components. The network may form part of the protective arrangement of Specification 902,998. Specification 903,000 also is referred to.