Distance protection of teed circuits

Multiended network interconnections, such as teed circuits, invariably pose special difficulties in their protection, and the methods of relaying that have been widely applied to plain feeders are often of limited applicability to circuits having more than two ends within the protected zone. Many of the difficulties and limitations have for long been acknowledged, and the paper seeks to extend the investigations hitherto recorded, by providing a detailed account of the range of relaying conditions encountered in different system configurations, in relation to the application of distance protection. The factors influencing the measurement of circuit impedance using local-end relaying signals at the three network terminals are examined, and means are advanced by which the loci of impedances presented to distance protection on the faulted and healthy circuits of single- and double-circuit teed interconnections may be evaluated for different types of fault. The limiting conditions of assessment in the predetermination of the settings and characteristic shapes of direct intertrip and blocking schemes are formulated, and the basis is given of a computer method by which the most advantageous settings may be secured, subject to constraints derived from the interconnection to be protected and the range of prospective fault levels at its terminations.