205 / 2022-03-14 18:33:03

Effects of Crosslink Coagent on the Conductivity and Breakdown strength of XLPE

cross-linked polyethylene,conductivity,crosslink coagent,DC breakdown strength

Inhibit Temperature Sensitivity of Conductivity in Crosslinked Polyethylene Modified by Crosslink Coagent

Xu Yang, Chunyang Li, Xingdong Zhao, Hong Zhao, Xuan Wang

Harbin University of Science and Technology

hongzhao@hrbust.edu.cn

Purpose/Aim

Cross-linked Polyethylene (XLPE) has been widely used as insulation material in power cables. However, in order to ensure high crosslinking degree of insulation, the content of peroxide initiator crosslinking agent in the formula system is too high, which leads to the generation of a large number of byproducts in the crosslinking process. Some of these cross-linking byproducts cannot be discharged through the degassing process, resulting in impurities and micropores in the cable insulation, endangering the long-term safe operation of the cable. Meanwhile, the byproducts will abate the low-temperature conductivity of the insulation through their polarity, improve the high-temperature conductivity by dissociation. This increases the temperature sensitivity of XLPE conductivity, result in a stronger electric field reversal. In order to reduce the excessive initiator content in traditional peroxide crosslinking, trimethylolpropane trimethacrylate (TMPTMA) has selected as a coagents of crosslinking. The thermal elongation, molecular structures and conductivity was tested.

Experimental/Modeling methods

The melting blend and hot-pressing approaches are employed in synthesis of XLPE-TMPTMA with the original materials. Complying to the standards of IEC 60811, the crosslinking degree of XLPE is tested by thermal elongation. The molecular structures of prepared samples are characterized by Fourier Transform Infrared (FT-IR). Electrical conductivity is measured by a three-electrode system at variable temperatures from 30 to 90 °C, and the electric field at each point covering the range of 5–40 kV/mm is applied for 60 min to measure the stable conductance current. The DC dielectric breakdown strength (DBS) were tested at 30 °C, 50 °C, 70 °C and 90 °C respectively.

Results/discussion

The thermal elongation results indicate XLPE-TMPTMA has sufficient crosslinking degree. The FTIR results prove that TMPTMA have been grafted onto PE molecules. The electrical conductivity results show that with the introduce of TMPTMA, at 20 kV/mm, the difference of conductivity between 30 °C and 90 °C decreases significantly. DBS test shows thatXLPE-TMPTMA materials exhibit evidently higher DBS than XLPE

Conclusions.

On the premise of ensuring the degree of crosslinking, the use of crosslinking coagent can reduce the amount of DCP. The temperature sensitivity of conductivity in XLPE can be reduced by crosslinking coagent.