Single Phase-to-Ground Faults Group Protection Algorithm Based on Zero-Sequence Current Correlation Coefficients for 6–35 kV Distribution Networks

Single phase-to-ground faults are predominant ones in 6–35 kV distribution networks with cable lines. The primary purpose of protection in such networks is to detect the fault occurrence and its location. However, it should be noted that not all algorithms function correctly in all possible operating modes. Most algorithms fail to identify the fault location due to intermittent arc faults. In underground distribution networks with a complex topology, the protection efficiency is known to decrease. This paper proposes a group protection algorithm based on the correlation coefficients of zero-sequence currents between adjacent feeders, implemented in the Matlab/Simulink environment. The algorithm has been developed based on the characteristics of zero-sequence current during single phase-to-ground faults with various types of neutral grounding. The developed algorithm allows for the identification of the moment a single phase-to-ground fault occurs in the distribution network, as well as the faulted feeder. The efficiency of the protection algorithm was verified using a model of a branched network with five feeders. During the study, three types of faults were modelled: steady and intermittent, according to two arc extinction theories (Petersen's and Petersen-Slepian's). Various sample rates of current were also tested to determine the correct operation of the algorithm within the device.