Study On Epoxy Insulation Impregnating Varnish For High-Voltage Motors

For large motors or generators, voids may reduce useful life of the insulation as a result of breakdown under high electrical stress. V.P.I impregnating varnish can produce continuous insulation system without voids, which offered components with good heat conductivity, thus improved economic indicator and reliability of motor performance.This work focused on preparing two novel compositions of epoxy insulation impregnating varnish for high-voltage motors. One comprised of diglycidyl ether of bisphenol A (DGEBA) and styrene as reactive diluent, the other composition based on alicyclic epoxy and with glycidol ether H8 as diluent. Thus, a variety of effects on properties of the two compositions were investigated, especially the relationships between chemical structure and properties of cured products.As for DGEBA/ anhydride / styrene composition, FTIR was utilized to trace the reactions and the reaction mechanisms were discussed. The prescription was optimized in accordance with analyzing dielectric performance behaviors, it was comprised of 100 parts DGEBA, 30 parts styrene, MA, accelerator BDMA and AlAcAc respectively were 3.75,0.3 and 0.2parts, MHHPA was 80 parts.The alicyclic epoxy / anhydride / H8 composition was studied the effect of contents of accelerator AlAcAc, diluent H8, and different equivalent proportion of epoxy/anhydride on the curing process, the network and the property of the products. Based on the property analyzes yielded the optimum prescription: the equivalent proportion of epoxy/anhydride was 1:0.8, AlAcAc was 0.5 parts, H8 was 15 parts. This prescription was of low viscosity at room temperature for easy flow, which was 56 cps. The kinetics of the curing processes of optimum prescription was analyzed by Kissinger and Crane equations, and discussed the curing kinetic parameters of the curing systems: the activation energyâ–³Ea=48.3kJ/mol, the reaction order value n=0.86.Because the behavior of thermosets was affected by the addition of diluents, it is important to investigate the changes taking place during the thermal degradation of the material. We studied the thermal property of epoxy compositions without diluents and with 15parts H8 through TGA. The two TGA curves were similar, which indicated there was no obvious difference on thermal stability. The kinetic parameters was extracted from TGA thermal degradation experiments, analyzed by Kissinger method and Flynn-Wall-Ozawa method, Both the results showed that the activation energy of composition with 15 parts H8 was lager than the composition without diluent, which meant the composition with 15parts H8 was more stable in the fastest degradation stage, thus H8 was a suitable choice for impregnting vanish composition.