Effect of radical scavenger on electrical tree in cross-linked polyethylene with large harmonic superimposed DC voltage

In this study,three kinds of radical scavenger Chimassorb 944,Tinuvin 622,and Tinuvin 770 are used to suppress the growth of electrical trees in cross-linked polyethylene(XLPE)with transient superimposed voltage under the temperature gradient.The tree morphology,tree length,accumulated damage,and time to breakdown are used to investigate the effect of radical scavenger on the electrical treeing process.It is found that under the temperature gradient caused by the temperature rise on the high voltage side,only Tinuvin 622 can always suppress the electrical tree as the temperature gradient rises.Under the temperature gradient caused by the temperature rise on the ground side,the three radical scavengers can all suppress the electrical tree.The breakdown of electrical tree exhibits the strong DC polarity dependence.Meanwhile,energy levels of these three radical scavengers are calculated through quantum chemistry,and the results indicate that radical scavengers have greater electron affinity,smaller ionisation energy,and smaller energy gap than XLPE.According to the surface potential decay test results at 60℃,it is found that all three radical scavengers can introduce deep traps.The different performances of radical scavengers under different temperature gradients and voltages are determined by the trap distribution characteristics,the molecular structure and chemical reaction of the additives themselves.It is concluded that Tinuvin 622 has potential for use in high voltage direct current XLPE cable application.