Dielectric properties and thermal conductivity of micro-BN-modified LSR used for high-voltage direct current cable accessories

Thermal breakdown is the main form which leads to direct current (DC) cable accessories insulation invalid. In order to enhance the insulation of DC cable accessories, liquid silicone rubber (LSR) is improved by filling micron boron nitride (BN) to promote the dielectric properties and thermal conductivity in this paper. The electrical conductance, DC dielectric breakdown strength (DBS), dielectric spectrum and thermal conductivity of micro-BN/LSR composites with various filling concentrations are analyzed in combination with the charge-trap energy-level distributions by means of isothermal surface potential decay (ISPD) method. By filling micron BN into LSR, the insulation performance and thermal conductivity can be improved simultaneously, thus achieving a higher insulation reliability. When the concentration of BN micron-filler is increased to 40 wt%, the electrical conductivity can be reduced by three orders of magnitude compared with pure LSR, and the DC DBS and thermal conductivity rises by 52.82% and 141.38%, respectively, while the relative dielectric permittivity and dielectric loss are slightly increased. The ISPD analyses indicate that trap-level depth in BN/LSR composites can be further raised by increasing the concentration of BN micron fillers, thereby getting a higher DBS.