Investigating the influence of the lubricant coating on hypodermic needles on electrical tree characteristics in epoxy resin

Many electrical treeing studies have employed the use of hypodermic needles in the point-plane geometry configuration. These hypodermic needles developed for medical usage are coated with a transparent lubricant. Limited literature exists on sample preparation techniques addressing the removal of this lubricant coating, which affects adhesion of the epoxy resin to the hypodermic needle. In this experimental study, the impact of the lubricant coating on electrical tree growth and associated partial discharge activity was investigated. The findings confirm that the lubricant coating inhibits electrical tree growth resulting in limited spread of the electrical tree while yielding the occurrence of ´rabbit-ear´ partial discharge patterns. This study also reports pronounced visible gaseous activity upon electrical tree initiation in the presence of the lubricant coating. Electrical trees were developed using point-plane samples of LY/HY 5052 epoxy resin with a gap spacing of 2 ± 0.5 mm. All electrical trees were 50 Hz initiated at either 8.4 or 14.4 kV peak. After electrical tree initiation, 50 Hz composite waveforms incorporating harmonic content were applied as the excitation waveforms.