A new technique for setting distance protection and fault location by measurement of transmission line system impedance characteristics

This paper presents the methodology for a new technique to measure the impedance of transmission lines and the associated earth fault return paths. The test procedure is detailed, and practical results are presented from tests on a utility network. The procedure is critically examined for comparison with existing theoretical studies and other empirical methods to calculate distance protection and fault location settings. The significance of the varied quality and accuracy of the results from these existing techniques arises from the particular importance of the accuracy of the residual compensation or k-factor setting in preventing over- or under-reach of the protection of transmission line systems. The simple practical method presented has highlighted the limitations and the cost of failure of existing techniques, with major implications for improving the protection of, fault finding and fault-location on the electricity transmission network. Related testing proposals are also presented for further consideration, including direct measurement of substation earth mat impedance in electrically noisy environments.