Electrical and Physico-chemical Properties of XLPE Under Different Vulcanization Pressures for 500 kV EHVDC Cable Factory Joint

Vulcanization pressure is critical for the enhancement of electrical and physico-chemical properties of extra high voltage direct current (EHVDC) cable factory joints. In this study, microstructure and physico-chemical characteristics of 500 kV EHVDC cross-linked polyethylene (XLPE) cable factory joint under various vulcanization pressures were investigated. Particularly, their electrical performance was analyzed in terms of space charge, current density and AC/DC breakdown strength measurements. The results indicate that, with increasing of the vulcanization pressures, the cross-linking degree, crystallinity and AC breakdown strength increase continuously. Notably, the threshold field strength for the space charge injection and the DC breakdown strength increase up to 1.9 MPa and then decrease. Above 1.9 MPa, the cross-linking by-products introduce more shallow traps, whereas the lamella undergoes thermal expansion, which increases the interplanar spacing and leads to a significant accumulation of the space charge. It is found that the optimal vulcanization pressure in the EHVDC cable factory joint manufacture can enhance the electrical performance of the cable factory joint insulation.