硫化压力对500kV超高压直流XLPE海缆工厂接头交接层界面绝缘性能的影响OA

Extra-high-voltage direct-current(EHVDC)cross-linked polyethylene(XLPE)submarine cable factory joints play a central role in long-distance,high-capacity DC transmission systems.However,differences in thermal history during the manufacture of factory joints inevitably give rise to a transition interface between the main insulation and the return insulation,where space charge accumulation can trigger insulation degradation.As a result,the impact of vulcanization pressure on the dielectric behavior of factory joints must be properly evaluated in the development of 500 kV EHVDC submarine cable systems. Commercial XLPE pellets for 500 kV DC submarine cables were used to prepare XLPE transition-layer specimens by hot pressing method.Vulcanization pressures of 0.7,1.6,1.9,and 2.5 MPa were selected to match those employed in practical manufacturing of factory joints.The surface morphology and physicochemical properties of the specimens were characterized by scanning electron microscopy(SEM),differential scanning calorimetry(DSC),and gel content analysis.Electrical performance was evaluated via isothermal surface potential decay,conduction current density test,DC breakdown strength test,and pulsed electro-acoustic(PEA)test at 30,50,70,and 90℃,respectively.In addition,a bipolar charge transport model for a factory joint was developed.The model was validated through space charge measurements conducted on a full-sized factory joint,and the effect of vulcanization pressure on space charge behavior in full-sized factory joints was subsequently analyzed. The experimental results show that increasing vulcanization pressure enhances interfacial crosslinking and reduces the amorphous fraction in the specimens,leading to an increase in the energy level of deep electron traps and a reduction in the energy level of deep hole traps,accompanied by an increase in carrier mobility.At a vulcanization pressure of 1.6 MPa,the specimens exhibit the maximum DC breakdown strength at elevated temperature,and a pronounced improvement in interfacial space-charge distribution is observed.When the pressure exceeds 1.6 MPa,interfacial crosslinking continues to improve;however,microvoid defects generated by decomposition of crosslinking by-products increase the amorphous fraction.Consequently,the DC breakdown strength and the space-charge injection threshold decrease significantly,and carrier mobility is simultaneously reduced,leading to pronounced space-charge accumulation at the transition interface.Space charge measurements on the factory joint revealed that the potential barrier formed at the interface between the main insulation and the return insulation inhibits carrier transport,leading to accumulation of positive charges at the interface.The simulated space charge distribution of full-sized factory joint was in close agreement with the experimental observations in both magnitude and spatial location.Simulation results for the full-sized factory joint further demonstrate that space charge accumulation preferentially occurs at the composite interfacial regions located at both ends of the stress cone.An elevated temperature accelerates carrier injection and space charge accumulation,resulting in pronounced electric field distortion at the interfaces. Based on the results,an appropriate vulcanization pressure of 1.6 MPa is beneficial for improving the interfacial dielectric performance of factory joints,and space charge induced insulation degradation at interfaces should be considered in the design and development of EHVDC submarine cable factory joints.