Adaptive Protection of Partially Coupled Transmission Lines

The mutual coupling effect in parallel transmission lines renders the maloperation of conventional distance relays and makes it more difficult for power system operators to establish a reliable operation of transmission systems. This paper presents an adaptive protection system approach to improve the performance of conventional distance relays in partially coupled transmission lines. The conducted study deals with single-line-to-ground faults and the proposed algorithm is designed for ground distance units. The mutually coupled transmission lines, which are not terminated in same substations, are studied and the impedance estimated by associated distance relays is corrected through revising the level of zero sequence compensation. The compensation term is calculated based on the system equivalent sequential networks and it is substituted in an iterative process for enhancing its accuracy. The proposed approach can offset the fault resistance effect to calculate an accurate fault impedance. The proposed approach lies in the local protection category and utilizes local and very limited remote data for decision making. Simulation results present the adaptive features of the proposed protection scheme. Besides, practical applications of the proposed approach are demonstrated and analyzed through experimental studies by developing a prototype on a MCU (LPC2368_ARM7TDMI) processor.