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Influence of inter-line faults on distance protection in parallel lines

The conventional configuration pattern of relaying protection was challenged by parallel transmission lines inter-line faults, which produced an apparent effect on the distance protection. It was absolutely essential to study parallel transmission lines inter-line faults and their influence on distance protection. The analytical analysis method of parallel transmission lines inter-line faults for relaying protection was presented in this paper, which could accurately analyze the influence tendency and boundary of inter-line faults on the main distance element. So as to extract related fault characteristic by using current branch coefficient to study the influence, fault port equivalent impedance was solved by injecting current on the zero sequence mutual inductance decoupled model, and the analysis of different types inter-line faults were dealt with, combining the way of zero sequence current controlling voltage source with the fault boundary conditions. The research result indicated that the distance protection would not exceed the first part of distance value when the inter-line grounding faults occurred, and the inter-phase measure impedance calculated with twice current of fault phase would reflect the actual measure impedance more accurately when the inter-line faults occurred without grounding. With the simple calculation and the clear physical conception, the proposed analytical analysis method also was fit to study the influence of inter-line faults on the phase element and other protection elements, and could be applied to the calculation and analysis of multi-circuit parallel lines inter-line faults. Considering the influence of mutual inductance intensity, difference between both sides power source, fault location and other related factors, it could definitely and accurately analyze protection range with the analytical expression, which provided the theoretical basis for the setting and disposition of relaying protection. Finally, the analysis result was verified by the example of Guangdong power grid.