Improve The Reliability Of Extrusion Molded Joints Of High Voltage Submarine Cables

Limited by the production process,the length of a single submarine cable often cannot meet the actual distance requirements for cross-sea connections.Extruded molding joint(EMJ)can connect multiple XLPE submarine cables that do not meet the length requirement.Compared with prefabricated joints,EMJ has many advantages such as the recovery insulation material and the insulation material of the cable,the joint outer diameter is similar to the cable outer diameter,and the excellent aging resistance and mechanical properties.The EMJ bulk insulation has been transformed into a three-dimensional network structure through dry cross-linking,which cannot be completely integrated with the recovery insulation.The resulting recovery insulation and bulk insulation interface area is the weakest link in the entire structure,which affects the operation of EMJ reliability.In this paper,the operating reliability of EMJ is improved from the perspective of process and material modification.In terms of improved processing technology,this paper proposes a glass fiber/epoxy resin composite preheated injection mold based on magnetic induction heating.The mold preheating type test results show that the glass fiber/epoxy mold can heat the mold itself and the conductor core together.If the core heating rate is too fast,an on-off heating method must be used to ensure the uniformity of the overall temperature of the device.The temperature distribution simulation results of the type test device show that the temperature rise of the EMJ body insulation reaction force cone is slower and the uniformity is poor compared with the glass fiber/epoxy mold and the conductor core.However,the temperature control method mentioned above can be used.After 160 minutes of preheating,the overall temperature of the device is maintained within the optimal extrusion temperature range,which can ensure good interface integration and improve the reliability of EMJ operation.The results of the die extrusion type test show that the temperature distribution of the die device during the extrusion process is reasonable and can meet the requirements of the extrusion temperature.The pressure in the extrusion process is maintained at about 1MPa,which meets the requirements of extrusion pressure.The entire preheating injection molding process lasts for 190 minutes,and the heating efficiency is greatly improved compared with the traditional mold that takes 1 to 2 days to complete the preheating injection molding process.After extrusion molding,an optical microscope was used to compare the sample at the interface between the body insulation and the recovery insulation and the sample at the interface of the traditional mold for preheating injection molding.The sample of the mold has no obvious defects,which can prove that the interface fusion of the mold is better than that of the traditional mold.In terms of material modification,this paper proposes to use nano-Si O₂modified XLPE and graft voltage stabilizer AOHBP modified XLPE as recovery insulation materials to improve the overall electrical tree resistance of the interface area of EMJ.In order to simulate the growth of electrical tree from the body insulation to the interface,this paper uses the fusion hot pressing method to prepare"6+2"double-layer insulation samples and conduct AC tree growth experiments.The experimental results show that EMJ recovery insulation can improve the overall resistance to electrical branches in the weak area of EMJ,whether nano-Si O₂modified XLPE or voltage stabilizer AOHBP grafted XLPE is used.Among them,0.4phr AOHBP grafted modified XLPE has the best ability to inhibit electrical branches.good.In order to simulate the situation of electrical tree insulation and recovery of insulation growth at the interface,the 0.4phr AOHBP grafted modified XLPE,which has the best performance in inhibiting electrical tree,was used to reproduce the"4+4"double layer by the melting and hot pressing method.The samples were insulated and the AC tree growth experiment was carried out.The results show that whether electrical tree is caused by the body insulation or at the interface,insulation recovery with 0.4phr AOHBP grafted modified XLPE can greatly improve the overall electrical tree resistance in the interface area of EMJ,thereby ensuring the reliability of EMJ operation.