An interline fault equivalent algorithm for common-tower double-transmission line with narrow line-to-line distance

Interline fault of double circuit line on the same tower is difficult to calculate and qualitatively analyze. To solve the problems and meet the need for qualitative analysis in relay protection research, an interline fault algorithm based on equivalent fault simplification is presented. Based on the character that coupling of lines is similar to that of phases on common-tower parallel lines with narrow line-to-line distance, the parallel lines’ model can be simplified using the average mutual inductance. Via equivalent simplification, the interline fault can be simplified to a virtual single-circuit-line fault form for calculation, and the achieved electric quantities can be used in the original network for calculating those of the parallel lines. And via comparing calculation results under new algorithm to those of ATP-EMTP simulation, it shows the new interline fault algorithm which uses the average mutual inductance is efficient and practical. And using the model of parallel-line with narrow line-to-line distance can correctly reflect most interline faults’ characters in practice and bring a more simple calculation process.