Spraying Core–Shell ZnO To Achieve High Insulation Performance for HVDC Cable Factory Joints

The interface insulation plays a key role in the long-distance high-voltage direct current (HVDC) cables. In this paper, four core–shell ZnO suspensions formed by different alkane coating were prepared for spraying on the factory joint interface. The chemical, electrical, and simulation studies were performed on synthesized nanoparticles and factory joint samples. Results show that the alkane-coated ZnO exhibits a noticeable surface halo and the thermal weight loss ratio increases with the increase of the alkane chain. Moreover, with the increase in the sprayed C1-ZnO concentration (coated by trimethoxymethylsilane) from 0.005 to 0.1 wt%, the insulating properties of the samples show an increasing trend at first and then decrease. Furthermore, as the encapsulated alkane chain increases, a very small concentration of 0.01 wt% of ZnO suspension (C6-ZnO) coated with hexyltrimethoxysilane was found to be a highly effective spray reagent, which can significantly reduce the DC electrical conductivity, increase the DC breakdown strength, and remarkably inhibit the space charge accumulation at the interface. The microscopic characterization showed a good dispersion of nanoparticles at the interface. The space charge simulation and molecular simulation results elucidated the mechanism of the interfacial nanoparticles to suppress the space charge and insulation property improvement. This approach provides a new solution for realizing 500 kV or higher voltage DC cables to achieve long-distance connections and breakpoint repairs or improve other polymer interface insulation.