Microstructural tailoring of XLPO for enhanced DC conductivity characteristics in HVDC cable insulation

The regulation of electrical conductivity characteristics is crucial in developing high-performance high-voltage direct current (HVDC) cable insulation to achieve a uniform and stable electric field distribution. The ideal DC conductivity characteristics for HVDC insulation should include low magnitude, thermal stability, and a suitably high voltage coefficient. Conventional crosslinked polyethylene (XLPE) insulation based solely on low-density polyethylene (LDPE) has stable crystallization and crosslinking properties, restricting modulation of its electrical properties. Accordingly, we propose a tailored design of crosslinked polyolefins (XLPO) characterised by synergistically enhanced electrical and mechanical properties, wherein linear low-density polyethylene (LLDPE) with varying molecular structures is blended to modulate the microstructure and thereby regulate DC conductivity characteristics. The results demonstrate that the thermal stability of the DC conductivity was improved for all XLPO samples compared to XLPE, with the maximum reduction in activation energy reaching 21.4 %. XLPO-A, featuring longer chains blended, increased the voltage coefficient of conductivity from 0.177 m/V to 0.201 m/V. In addition, XLPO-B/C, with shorter chains blended, reduces the DC conductivity by over one order of magnitude at elevated temperatures. This work demonstrates a promising route toward precise modulation of electrical properties to further optimize HVDC cable insulation.