Tree Growth Characteristics of Epoxy Resin in LN2 Under DC Superimposed Pulse Voltage

Chosen as an important insulation material of high temperature superconducting dc cable terminals, epoxy resin needs to address the challenge of the liquid nitrogen (LN
₂
) temperature and various kinds of voltage due to the special operating environment. The switching over voltage, lightning strike, and current impact will introduce the pulse voltage into the operation of the dc equipment, which makes it necessary to study the insulating characteristics of epoxy resin under dc superimposed pulse voltage condition. This paper investigates the electrical tree growth characteristics of epoxy resin with application of dc superimposed pulse voltage in LN
₂
. The tested samples were stressed with combined dc-pulse voltage with different amplitudes and polarities in a needle-plate geometry electrode system at -196 °C. Tree length and accumulated damage are employed to characterize the electrical tree. The experimental results indicate that when the dc and pulse voltage are of the same polarity, the rate of tree growth increases with the amplitude of dc voltage rising but would slow down after a period time of treeing. When the polarity of dc and pulse voltage is opposite, the growth rate decreases with the dc voltage amplitude increasing, while it could maintain a relatively high level during the whole treeing time.