Improved direct current electrical properties of XLPE modified by graftable antioxidant and crosslinking coagent at a wide temperature range

Abstract

Abstract To enhance the DC electrical performance of cross‐linked polyethylene (XLPE), the graftable antioxidant methacrylic acid 2‐hydroxy‐3‐(4‐anilinoanilino) propyl ester (GA), which contains carbonyl and amino groups, and the crosslinking coagent trimethylolpropane trimethacrylate (TMPTMA), which contains carbonyl groups, are individually or co‐grafted onto XLPE. The slightly higher deep trap density introduced by higher grafting concentration of TMPTMA results in more significant suppression effect of conductance current and enhanced breakdown strength at a lower temperature, while the suppression effect for the conductance current at 90°C becomes weakened due to limited trap energy. Meanwhile, the deeper energy level introduced by GA suppresses the conductance current and improves the electrical strength of XLPE at 90°C more significantly. By co‐grafting, the conductance current of XLPE in a wide range temperature can be significantly reduced, especially for the temperature dependence of conductance current, which is beneficial to suppress the field strength reversal. The results of thermally stimulated current and molecular simulation show that the polar groups of two monomers introduce deep charge traps in XLPE. The co‐grafting system ensures the rationality of the crosslinking reaction kinetics and does not affect the cable manufacturing.