Measurement of fault resistances in transmission lines by using recorded signals at both line ends

This article shows the results obtained by using a method for the calculation of fault resistances in transmission lines, like these resistances are really seen at the location of protective relays. The method is based on a well-known algorithm for fault location, which is complemented here in order to compute the fault resistances. The original algorithm for fault location only uses information from one line end, and it is applied twice here (once from each line end) in order to obtain the information to compute the fault resistances. For each fault, a fault resistance is computed from each line end, and the reported value is the average of both values if they satisfy the selected criterion of coherence (otherwise, the measurement is considered as no valid). This method was applied for the measurement of fault resistances for 70 actual faults, recorded at different voltage levels (230 kV, 400 kV, and 765 kV). The statistical behavior of these measured values shows that the fault resistances are moderate in a high percentage of cases. The knowledge about the statistical behavior of fault resistances is important for the protection of transmission lines, and these results can be complemented in the future by analyzing more data, in order to improve this knowledge. Other methods, based in other fault location algorithms, could be also applied in order to obtain the measured values of fault resistances from recorded data of real faults. The application of a criterion of coherence, for comparing the computed values of fault resistance from each line end, is a novel idea and it is important to consider the possible imperfections in the measurements and/or in power system models.