A new method for non-unit protection of power transmission lines based on fault resistance and fault angle reduction

In the paper, a new non-unit transient protection method suitable for single-phase faults of EHV power transmission lines was proposed based on the analysis of the propagation characteristics induced by fault transient current, the transition resistance and the fault angle on corresponding energy values of high-frequency transient current in extra high voltage (EHV) network. In the procedure, the transient current energy values from both sides of the bus were primarily normalized on the basis of transition resistance and fault angle, and then the characteristic value with functions of direction judge and value comparison was obtained by calculating their difference. By utilizing the characteristic value, the methodology came into being, by which the impacts of both transition resistance and fault angle were eliminated. The overall design has a high reliability level and owns twice the scope of the conventional protection. Simulations were performed and analyzed upon a three-phase 500 kV power system by utilizing ATP/EMTP, with various kinds of typical faults being taken into account. Plenty of results verify the feasibility of the algorithm for ultra-high speed protection of EHV power transmission lines.