Fault location for mixed two and three terminal overhead and underground cable transmission circuits

Locating a fault precisely on power transmission lines is highly advantageous to power utilities in expediting the repair of the faulted components, speeding up the restoration of power supply, thereby reducing outage time and the financial burden on utilities. Several fault location methods including impedance and traveling wave based are commercially available for conventional transmission lines. However, fault location in mixed circuits (combined overhead and underground/subsea cables) is difficult due to different impedance parameters for each section and lack of junction measurements. In this paper, innovative faulted section identification and fault location solution is developed using all side voltage and current measurements for two and three terminal mixed lines. Faulted section identification is very important input for the fault location solution. For two terminal mixed lines, faulted section is identified by checking the sign of the calculated faulted section identification indices. The faulted section identification indices are calculated using the ratio of difference of voltage and current at each junction of the mixed line. The junction voltage and current are calculated from both terminals using each section parameters and positive sequence voltage and current measurements. For three terminal mixed lines, faulted section is identified by comparing the differences of calculated and measured voltage at each terminal. The faulted location is calculated using the faulted section identification information, each section parameters and during fault phasors. The proposed solution is verified using laboratory experimental and field data and it is found to be accurate. The solution is implemented in the existing line differential relay platform using 1kHz sampling rate and it does not need any additional infrastructural changes.