Third Harmonic Current Phase Angle Behaviour During Branch Touching Wire Earth Faults

This research scrutinizes credibility of the third harmonic (I3h) current phasor relationship with respect to the fundamental voltage (V50-Hz) as a potential signature of Vegetation High Impedance Faults (VeHIFs) using data from continuous-contact ‘branch touching wire’ earth faults. Prior work argued on a distinct phasor relationship between I3hand V50-Hz. Common HIF models simulate this distinct phase relationship as ∼ 180° with near perfect stability after only few cycles. This work uses a dataset of 132 phase-to-earth (ph-to-e) VeHIF test recordings to analyse temporal variations in the I3hphase shift. The over-fault mean was ∼170° with a volatility (standard deviation (STD)) of 7°. Ninety-five percent of tests stabilised to these values within 1.25-s of fault inception. Outlier cases with long phase-shift stabilisation periods may pose a risk in the timely detection of earth faults. However, such cases were usually associated with low initial fault currents (If) for extended periods and were unlikely to cause ignition. Fault currents above 33mA are shown to have stable phase-shifts. Finally, a regressive statistical model is presented for modelling time sequences of I3hphase-shift with respect to V50-Hz.