Temperature-Dependent Space Charge and Electric Field Distributions in Polypropylene-Insulated Flexible Factory Joint for HVDC Cables

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This paper investigates the temperature-dependent space charge and electric field distributions in polypropyleneinsulated flexible factory joint (FFJ) for HVDC cables, with a particular focus on the effect of insulation interfacial region. The mechanism of interfacial charges on the electric field under different temperature gradients (ΔTs) is discussed. The interfacial charge distributions and trap characteristics are assessed using bilayer samples. Subsequently, an electro-thermal field and space charge coupling simulation model for FFJ with the interfacial region is established and experimentally validated, confirming its accuracy and reliability. The results indicate that, compared with the cable insulation (CI) and reinforcing insulation (RI), the interfacial region exhibits inferior insulation performance, which is a primary factor contributing to interfacial charge accumulation. At ΔT = 0 °C, interfacial charges increase the maximum electric field (Emax) in the FFJ by 14.12%. As ΔT increases, positive interfacial charges gradually dominate, leading to the position of Emax to shift from the CI to RI. Although the interfacial charges reduce the electric field within the interfacial region, they enhance the tangential electric field (Et) as ΔT rises. At ΔT = 30 °C, the maximum Et in the interfacial region increases by 52.26% compared with that at ΔT = 0 °C. These findings contribute to elucidating the FFJ failure mechanisms, providing a basis for improving submarine cable system stability and safety.