Improved body and interface properties of EPDM insulation for HVDC cable accessory by grafted voltage stabilizer

•Voltage stabilizer is simultaneously grafted onto EPDM macromolecule during crosslinking.•Mechanical strength and thermal stability of EPDM are improved.•Charge migration is inhibited by charge traps introduced by grafted voltage stabilizer.•Breakdown strength along EPDM/XLPE interface is significantly improved.•Internal and interfacial properties of EPDM/XLPE composite insulation are improved. As a key component in HVDC cable accessory, EPDM insulation is prone to breakdown both in body and along interface. To improve the comprehensive electrical strength of EPDM, voltage stabilizer 2-propenyl-4,6-dibenzoylresorcinol (ADR) was simultaneously grafted onto macromolecules through free radical reaction on its vinyl during crosslinking of EPDM. After modification, the mechanical strength and thermal stability of EPDM are improved. In terms of body properties, the injection and rapid transfer of space charge under normal electric field are weakened, the volume conductivity is reduced, the breakdown strength is improved and the growth of electrical tree is suppressed. In terms of interface properties, the normal electric field at the EPDM/XLPE interface is weakened, hence reduced potential risk of deterioration initiated from interface. Moreover, the surface conductivity of EPDM is reduced, the charge accumulation and migration along the EPDM/XLPE interface are suppressed, and the interface breakdown strengths under different interface pressures are significantly increased under tangential electric field. Molecular simulations and UV absorption characteristics indicate that the grafted ADR molecules not only introduce charge traps into EPDM, but also absorb the high energy from trapped electrons and consume it through multiple excitations, thus preventing the electron avalanche and subsequent degradation of EPDM. [Display omitted]