Fault resistance investigations for faults in double-circuit double-fed transmission lines

This paper presents investigations into the effect of the fault resistance on the fault current levels in double-circuit, double-fed transmission lines to highlight effects such as intercircuit mutual coupling and the remote source infeed. A current amplitude comparison algorithm that supervises all the six currents is used for the investigations. The investigations are based on different fault analysis, which involve different fault types at different locations, on a mathematical model line that simulates a typical double-circuit line configuration, employing a matrix-based three-phase analysis method. The algorithm uses the ratios between the magnitudes of the currents to detect the fault and to propose critical values of the ratios, as the suitable setting of the relay. It is found that, the maximum value of the fault resistance that could be detected is 170 Ω at 80% of the line length that increases to 730 Ω at relay location, which is equivalent to 5 to 21 times the positive sequence impedance of the considered line.