Investigating the impact of harmonics on the breakdown of epoxy resin through electrical tree growth

Abstract

Many studies have investigated the influence of harmonics on insulation life. A limited number of these studies address electrical tree growth characteristics while even fewer employ harmonics maintaining a constant peak voltage. This experimental study sought to quantitatively identify any distinguishing features of electrical tree growth characteristics as a consequence of harmonic content. The total harmonic distortion (THD) and waveshape (K <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">s</sub> ) indices were varied to a maximum of 40% and 1.6 respectively. Electrical trees were developed in point-plane geometry using 2 μm tip radius hypodermic needles and a 2 mm gap in epoxy resin (LY/HY 5052) samples. Upon electrical tree initiation, 50 Hz composite waveforms incorporating harmonic content were applied as the excitation waveform at a constant voltage of 14.4 kV peak for 2.5 hours. No change in the electrical tree growth characteristics was identified using the width/length ratio. Electrical tree growth resulting from low power quality reduced operational insulation life and decreased the Weibull shape parameter β with the 7 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">th</sup> harmonic displaying particular characteristics worthy of further investigation.