Epoxy resin-impregnated insulation paper (RIP) composites are used as the inner insulation of dry condenser bushing in the ultra-high voltage direct current (UHVDC) power transmission system. To improve the dielectric properties and heat conductivity of RIP, hexagonal boron nitride (h-BN) nano-flakes are added to the insulation paper at concentrations of 0–50 wt % before impregnation with pure epoxy resin. X-ray diffraction (XRD), scanning electron microscopy (SEM) observations, thermal conductivity as well as the typical dielectric properties of direct current (DC) volume conductivity. DC breakdown strength and space charge characteristics were obtained. The maximum of nano-h-BN modified heat conductivity reach 0.478 W/(m·K), increased by 139% compared with unmodified RIP. The DC breakdown electric field strength of the nano-h-BN modified RIP does not reduce much. The conductivity of nano-h-BN modified is less sensitive to temperature. As well, the space charge is suppressed when the content is 50 wt %. Therefore, the nano-h-BN modified RIP is potentially useful in practical dry DC bushing application.

Epoxy resin-impregnated insulation paper (RIP) composites are used as the inner insulation of dry condenser bushing in the ultra-high voltage direct current (UHVDC) power transmission system. To improve the dielectric properties of RIP, nano-SiO₂ is added to the insulation paper at concentrations of 0–4wt % before impregnation with pure epoxy resin. X-ray diffraction (XRD), scanning electron microscopy observations as well as the typical dielectric properties of relative permittivity, DC volume conductivity, DC breakdown strength, and thermally stimulated depolarization current (TSDC), were obtained. The effects of trap parameters on the breakdown field strength and volume conductivity were investigated. The DC breakdown electric field strength of the sample increased as the trap level increased. The maximum DC breakdown strength of nano-SiO₂-modified RIP was increased by 10.6% the nano-SiO₂ content of 2 wt %. The relative permittivity and DC volume conductivity were first decreased and then increased with increasing nano-SiO₂ content. These changes occurred near the interfaces between nano-SiO₂ and RIP. The increased DC breakdown strength was mainly attributed to the increased trap level.

High-voltage direct-current (HVDC) dry bushing capacitor-core insulation is composed of epoxy resin-impregnated insulating paper (RIP). To improve the thermal conductivity, breakdown strength, and space charge characteristics of RIP, 0.1 wt % nano-cellulose fiber (CNF)-modified RIP (CNF/RIP), 2.5–30 wt % hexagonal boron nitride (h-BN)-modified RIP (h-BN/RIP), and 2.5–30 wt % h-BN + 0.1 wt % CNF-modified RIP (h-BN + 0.1 wt % CNF/RIP) were prepared. Scanning electron microscopy (SEM) was implemented; the thermal conductivity, DC conductivity, DC breakdown strength, and space charge characteristics were tested. The maximum thermal conductivity of h-BN + 0.1 wt % CNF/RIP was 0.376 W/m.K with a h-BN content of 30 wt %. The thermal conductivity was 85.2% higher than that of unmodified RIP. The breakdown strength and charge suppression were the best in the case of 10 wt % h-BN + 0.1 wt % CNF/RIP. The maximum breakdown strength was 11.2% higher than that of unmodified RIP. These results can play a significant role in the research and development of insulation materials for HVDC dry bushing.

Octafluorocyclobutane (c-C₄F₈) is one of the environmentally friendly gases with the potential to replace SF₆. In this paper, the AC breakdown characteristics of c-C₄F₈/N₂ mixture in an extremely non-uniform electric field were studied; the effects of the gas pressure, electrode distance, and c-C₄F₈ volume fraction on the breakdown voltage were analyzed; and the feasibility of replacing SF₆ with c-C₄F₈/N₂ was verified. The results show that the breakdown voltage of c-C₄F₈ /N₂ increases with an increase in pressure, electrode spacing, and volume fraction of c-C₄F₈ in an extremely non-uniform electric field. Under the same conditions, the breakdown voltage of 20%c-C₄F₈/80%N₂ is 46–90% that of 20%SF₆/80%N₂. When the pressure is 0.3 MPa, the 20%c-C₄F₈/80%N₂ breakdown voltage can reach over 57% that of SF₆. Taking into consideration the environment, liquefaction temperature, and insulation strength, 20%c-C₄F₈/80%N₂ may replace SF₆ used for medium- and low-voltage equipment.