Experiments and Simulations on the Equivalence of Pre‐Cross‐Linking in Cable Insulation Material Extrusion

ABSTRACT The rheological properties of cable insulation materials are critical to the long‐term continuous extrusion performance of high‐voltage cables, with the pre‐cross‐linking effect playing a key role in determining the rheological behaviour of the insulation material during extrusion. Considering the pre‐cross‐linking effect, this study investigates the influence of molecular structure on the extrusion temperature, viscosity and shear rate distribution of insulation materials through equivalence experiments and simulations. The results indicate that the maximum temperature of 143°C occurs at the extrusion die land, where pressure and shear rate are highest. Furthermore, based on the optimised simulation model with experimental results, an empirical formula was established for predicting the maximum extrusion temperature of different insulation materials. This study reveals that although an increased terminal double‐bond content in low‐density polyethylene (LDPE) enhances the reactivity of insulation materials and reduces their shelf life, it also allows for a reduction in cross‐linking agent content, thereby mitigating pre‐cross‐linking. Insulation materials with a higher long‐chain branching degree and terminal double‐bond content in LDPE, combined with a lower cross‐linking agent content, are less susceptible to pre‐cross‐linking, which are more suitable for long‐length submarine cables, whereas the reduced by‐products also benefit the manufacture of DC cables; high‐speed shear promotes the diffusion of the cross‐linking agent dicumyl peroxide and enhances its interaction with the polyethylene chains. This research elucidates the influence of pre‐cross‐linking on the extrusion performance of insulation materials and develops an insulation material formulation more suitable for long‐duration extrusion.