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Those transmission lines that are on the same tower present unique problems to distance relays, especially for cross-country faults. In this paper, a novel first-zone distance relaying algorithm of parallel lines using only single-line sampling data is proposed for cross-country nonearthed faults. The relation between six phase currents and six sequence currents of parallel lines is derived. Moreover, the sequence currents of the adjacent parallel line at the relay location are expressed only by the sequence currents of the concerned line. Finally, the distance relaying algorithm using the one-end sampling data from the concerned line is presented. The computer simulations with PSCAD/EMTDC software and practical transmission-line parameters are carried out. The results show that the proposed algorithm can obtain the accurate measuring impedance for cross-country nonearthed faults and the accuracy is not affected by fault resistances, load currents, and source impedances. [ABSTRACT FROM AUTHOR]

In order to accurately measure the impedance, the residual current for impedance measurement in ground distance relay is compensated in a fixed manner. It has been shown that the above compensation manner may have negative impact on the phase selection in mho elements in a single-pole trip scheme. A new residual current compensation method based on the magnitude of current of each phase for mho elements is presented in this paper. The performance of this new method is analyzed under all kinds of fault conditions. Simulation studies are carried out to investigate the new compensation method based fault component impedance relay in a typical transmission system. The relay has shown satisfactory performances under various fault conditions especially for the close-in ground fault and cross-country fault. This new compensation method can also be used in phase selector based on impedance measurement. [ABSTRACT FROM PUBLISHER]