| With the development of electric power system, requirements for the protection devices are becoming higher and higher. More and more new methods and principles are applied to the protection devices. Based on the study of traditional transverse differential protection, regarding to the characteristics of parallel double-lines, this paper presents a new parallel double-lines protection principle based on sampling correlation. The correctness of the theory has been proved by simulation tests. With the building of double-circuit and multi-circuit lines, the effects on the line protection because of zero-sequence mutual inductance between the circuits should not be neglected. The paper analyzes and derivates its effects on the error of measuring impedance. In allusion to the malfunction phenomenon of the longitudinal direction protection, the improved method based on sampling correlation is presented. Considering the importance of single-phase automatic reclosing to the reliability of electrical power system, the paper distinguishes the permanent and the transient fault in the case of single-phase grounding based on the improved correlation coefficients and realizes correct and reliable single-phase automatic reclosing.
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