Nonlinear Ethylene Propylene Rubber And Its Application In DC Cable Accessories

As an important part of DC transmission system, crosslinked polyethylene(XLPE) insulated high-voltage DC cable is increasingly applied in recent years. Cable joint and terminal is the core of power cable system accessories and the weakest link in high voltage dc cable systems. Due to the electric field distribution under DC voltage depends on the conductivity of material, and electrical conductivity is affected by temperature and electric field, which makes the electric field distribution in cable accessories very complicated. When the cooperation of electrical conductivity of the insulating materials in cable accessories is unreasonable, the electric field distribution will be distored, which could seriously affect the running stability of the cable accessories. This, to some extent, limits the XLPE insulation high-voltage dc cable line construction and development. Therefore, to develop the formula system of reinforced insulation material which has the ability to improve the electric field distribution of the cable accessories is of important application value.To improve the electric field distribution of the cross-linked polyethylene(XLPE) insulated high voltage direct current(HVDC) cable intermediate joint, nonlinear EPDM rubber composite materials for cable joint stress control body are prepared by adding nano-fillers. First of all, nano SiO2 is added to improve mechanical properties of EPDM material. And on this basis, inorganic nano filler such as graphite, nano carbon black are added to improve the conductivity properties of EPDM composites. Based on the tested conductivity characteristics of the composite materials, an HVDC cable joint simulation model is established to calculate the electric field distribution of cable joint and terminal. The results indicate that adding an appropriate mount of nano SiO2 can improve the mechanical properties of EPDM composites, when the content of nano SiO2 is 8 PHR, the mechanical strength meet the requirement. On this basis, adding nano carbon black and nano graphite can both improve the electrical conductivity of EPDM composites, with the increase of nano carbon black content, the conductivity increases gradually. With the increase of nano graphite content, the conductivity fell back slightly after rising first. With the improvement of temperature, the conductivity of EPDM composites with the same proportion increases with the temperature increasing. Nano carbon black/Si O2/EPDM composite and nano graphite/SiO2/EPDM composite with appropriate conductivity properties can effectively inhibit the space charge injection, and the electric field distribution is reasonable, the highest field strength point always stays in the XLPE cable insulation, the composites are suitable as the reinforced insulation in cable accessories.