Characterization of Heat-Resistant Insulating Impregnating Varnish Based on Bismaleimide/Diamine Copolymer

Abstract

With the development of high-voltage electrical equipment towards the direction of higher power density and higher voltage level, it will resulting in the temperature-resistant grade of insulating dip varnish. Bismaleimide (BMI) resin used as the matrix resin of dip varnish solution is widely applied due to its good aging resistance, mechanical properties and dielectric properties. Due to the imide ring structure in BMI resin structure, the bonding energy of chemical bonds in the molecule is higher. The resin reacts less at lower temperatures, resulting in the difficulty of forming and processing. The high crosslinking density of condensates results in unsatisfactory mechanical properties of BMI resin and presents a poor toughness. Therefore, this paper uses Michael addition reaction to prepare branched resin with large free volume from binary amine and BMI resin, and explores various properties of its cured products. The results show that: Using different kinds and different contents of binary amines, its insulation performance was further improved. MT-cured sample had the best comprehensive performance, with a minimum dielectric constant of 3.24. The minimum dielectric loss of BAPP cured sample was 0.00135. The maximum volume resistivity of FDA sample was 2.46×1015 Ω·m and the maximum breakdown field strength of BAPP sample was 29.83 kV/mm; The mechanical properties were significantly improved, and the maximum mechanical strength of the MT samples reached 174.63 MPa.