The Impact of Crosslinking Degree on DC Conductivity of LLDPE Based Insulation Materials

Owing to its longer backbone, shorter branched chain and lager node spacing, crosslinked linear low-density polyethylene may provide better electrical, mechanical and processing properties compared with low-density polyethylene (LDPE). Therefore, the possibility of using LLDPE as XLPE cable insulation material is considered. In this paper, the effect of crosslinking degree on DC conductivity of LLDPE materials is investigated. By controlling the mass fraction of crosslinking agent, four kinds of samples are prepared. The conductivities are investigated at different temperatures under 20 kV/mm electric field, which decrease with crosslinking degree increasing. In comparison with LDPE, it is found that under the same mass fraction of crosslinking agent, the DC conductivity of LLDPE is significantly lower than that of LDPE. Thus, LLDPE based XLPE cable can greatly reduce the heat loss in the process of DC transmission, improve the efficiency of insulation and avoid thermal breakdown. Moreover, DSC and infrared absorption spectra are experienced and the crystal structure are observed. The decrease of crystallinity and melting point with the increase of crosslinking degree indicates that crosslinking retards the crystallization process. In addition, larger and more inhomogeneous crystal cells are observed in the samples with higher crosslinking degree.