Effects of Pre-crosslinking on the Aggregate Structure and Space Charge Properties of XLPE

In the extrusion process of cross-linked polyethylene (XLPE) cables, when the local extrusion temperature is higher than the decomposition temperature of the cross-linking agent, the cross-linking agent will be thermally decomposed in advance, resulting in a low degree of pre-crosslinking of the material. In order to study the effect of pre-crosslinking on the space charge characteristics of XLPE DC cable materials, this paper carried out low-level pre-crosslinking treatment at different temperatures before the high-temperature cross-linking of the material. The aggregate structure of the material was characterized by means of scanning electron microscopy (SEM), differential scanning calorimetry (DSC) and cross-linking degree test, and the space charge characteristics at different temperatures were studied. The experimental results show that pre-crosslinking will reduce the crosslinking degree of XLPE on the one hand, and also lead to the decrease of crystallinity and the reduction of spherulite size. The changes of the aggregate structure make it easier to inject the homopolar charges in pre-crosslinked XLPE samples. Under the high temperature, the residual impurity molecules in the sample will also dissociate, generating a large number of the heteropolar charges, resulting the occurrence of severe electric field distortion.