An investigation of the harmonic impact on electrical tree growth

An electrical tree is a facet of an electrical ageing mechanism induced by electrical stress. In power networks and even in laboratory research the quality of applied sinusoidal electrical stresses (voltage) can be very varied, although it is not often monitored. This experimental study sought to identify any distinguishing features of electrical tree growth characteristics due to harmonic content. The impact of varied harmonic content superposed on the power frequency on electrical tree growth has been investigated. The total harmonic distortion (THD) and waveshape (K_s) indices were varied to a maximum of 40% and 1.6 respectively. Electrical trees were developed in point-plane geometry epoxy resin (LY/HY 5052) samples using 2 μm radius hypodermic needles and 2 mm gaps, at a constant voltage of 14.4 kV peak. Progressive measurements of the electrical tree growth width/length ratio were plotted and analysed as functions of the distortion indices. The results illustrate no distinct detectable change in electrical tree growth as a consequence of varied harmonic content at constant peak voltage.