Conductivity and Breakdown Properties of Epoxy Resin for HVDC Bushing by Multifunctional Modifier

In this paper, multifunctional epoxy-based additives of tri-glycidyl para-amino phenol (TGAP) and 4,4-tetraglycidyl diamine diphenol methane (TGDDM), with high heat resistance, are used as network modifier to tailor insulation performance of the traditional bisphenol A epoxy resin (DGEBA). The temperature-dependent DC conductivity and dielectric breakdown strength of cured epoxy resin before and after modification are investigated. Compared with the unmodified sample, the modified epoxy resins show higher conductivity at lower temperature, which is attributed to the increased carrier numbers and narrower forbidden bands of the multifunctional epoxy resins. However, at higher temperature, due to the larger energy level trap density and enhanced crosslinking density, the multifunctional modifier can reduce the conductivity and improve the breakdown strength of the DGEBA. At 120 °C, with addition of 10% TGAP, the breakdown strength is increased by 19.9%. Besides, the temperature coefficient of the conductivity for epoxy resin is reduced, which could improve the electric filed distribution and attenuate the maximum electric field strength influenced by the temperature gradient within bushing insulation, making the modified epoxy resin more suitable for the bushings for DC application.