Analysis of higher voltage harmonics at an early stages of single line-to-ground faults in electrical distribution grids

The study aimed to assess the feasibility of using higher phase voltage harmonics as a means of detecting single-phase faults at an early stage of their development. An analysis of oscillograms obtained during emergency events was carried out for the medium-voltage distribution grids of Kaliningrad Oblast. The oscillograms were obtained using reclosers for the period from 2018 to 2023. Out of over 2,000 recorded oscillograms, the phase voltage oscillograms corresponding to the gradual development of a single line-toground fault were selected. These oscillograms were harmonically analyzed using the fast Fourier transform algorithm. The results of this analysis showed that the third voltage harmonic distortion begins to increase steadily several industrial frequency cycles before the occurrence of a single line-to-ground fault. The study revealed that in over half of the cases, the third phase voltage harmonic distortion exceeds the value permitted by the power quality standard as early as 200 ms before the fault occurs. Starting from 110 ms, the number of such exceedances reaches 75%. The identified regularity can be used to improve automatic grid restoration systems and protection against single line-to-ground faults. An increase in the third phase voltage harmonic can serve as one of the early signs of a single-phase insulation fault in power grid equipment and can be used to preventively run algorithms for localizing faulty grid sections as part of developing adaptive protection against single line-to-ground faults.