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

This research scrutinizes credibility of the third harmonic (I<sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3h</sub>) current phasor relationship with respect to the fundamental voltage (V<sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">50-Hz</sub>) 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 I<sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3h</sub> and V<sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">50-Hz</sub>. 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 I<sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3h</sub> phase 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 (I<sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">f</sub>) 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 I<sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3h</sub> phase-shift with respect to V<sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">50-Hz</sub>.