Charge Suppression and Breakdown Characteristics Improvement of Factory Joint for Submarine Cable by Atmosphere Pressure Plasma Jet

High-voltage direct current (HVDC) submarine cable factory joint (FJ) is the core component to realize the flexible connection of multi-segment submarine cables and meet the requirements of large-length cross-sea transmission distances. However, charges tend to accumulate, and even lead to breakdown at the interface between cable insulation (CI) and reinforcing insulation (RI) due to the weakness of the interface region. In this paper, an atmosphere pressure plasma jet (APPJ) reaction system is built to treat double-layer flat samples and coaxial cylindrical samples respectively, which effectively suppresses the interface charge and enhances both the normal and tangential breakdown strengths. Scanning electron microscope (SEM) is used to observe the optimization of interface morphology. Pulsed electro-acoustic (PEA), Direct Current Integrated Charge (DCIC), thermally stimulated depolarization current (TSDC) and breakdown strength characterize the interface charge and breakdown properties. The results show that plasma reduces the microdefects in the interface, thereby, on the one hand, suppressing charge accumulation by 39 %; on the other hand, it increases the normal and tangential breakdown strengths of the interface by 5.4 % and 6.8 %, respectively. Moreover, in the DCIC test, the space charge accumulation and conduction of current are quantified. Specifically, 15-minute plasma treatment reduces <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$Q_{\text {space }}$</tex> and <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$I_{\text {cond }}$</tex> by 95.8 % and 53.9 %, respectively. The interface treatment technology of FJs based on APPJ proposed in this paper can lay a theoretical foundation for the future development of supporting devices.