en05000220.vsdRZmARGLdARGLdARGLd ARGLdRLdFwRLdRvZLIEC05000220 V1 EN-USFigure 111: Characteristic for zone measurement for a long line8.3.2.6 Parallel line application with mutual coupling M17048-417 v2General M17048-567 v3Introduction of parallel lines in the network is increasing due to difficulties to getnecessary area for new lines.Parallel lines introduce an error in the measurement due to the mutual couplingbetween the parallel lines. The lines need not be of the same voltage in order toexperience mutual coupling, and some coupling exists even for lines that areseparated by 100 meters or more. The mutual coupling does influence the zerosequence impedance to the fault point but it does not normally cause voltageinversion.It can be shown from analytical calculations of line impedances that the mutualimpedances for positive and negative sequence are very small (< 1-2%) of the selfimpedance and it is a practice to neglect them.From an application point of view there exists three types of networkconfigurations (classes) that must be considered when making the settings for theprotection function.The different network configuration classes are:1. Parallel line with common positive and zero sequence network2. Parallel circuits with common positive but isolated zero sequence network3. Parallel circuits with positive and zero sequence sources isolated.1MRK 506 369-UEN B Section 8Impedance protectionLine distance protection REL670 2.2 IEC 217Application manual
