Breakdown strength-enhancing study on anti-corona nonlinear material for high-voltage generator stator coils

The insulating structure near the slot outlet of high-voltage generator stator coils is the typical bushing structure, which is prone to corona and has a decisive impact on the safety of the generator. In engineering, nonlinear resistance anti-corona tapes are usually bound with around the main insulation surface of the stator coils near the slot, to achieve the effect of homogenizing the electric field. Usually, the resistance nonlinearity is increased by adding semi conductive or conductive materials into the anti-corona tape. However, after the process of adding semi conductive or conductive materials, the breakdown strength of anti-corona tape is often reduced, resulting in that anti-corona tapes with good nonlinear cannot be applied. In order to have both good nonlinear resistance and breakdown strength, epoxy resin (EP) is used as a matrix, which is blended with one-dimensional structured carboxyl-functionalized multi-walled carbon nanotubes (MWCNTs) and zero-dimensional structured polyaniline (PANI) to obtain nonlinearly good materials in this paper. The nonlinear conductivity characteristics and breakdown characteristics were tested separately. The results show that compared to MWCNTs/EP composite materials, PANI-MWCNTs/EP composite materials have higher nonlinear coefficients and breakdown strength. The breakdown field strength of 0.5wt% MWCNTs/EP composites is 2.11 kV/mm, and the nonlinear coefficient is 1.41. In contrast, the breakdown field strength of 3wt% PANI-0.5wt% MWCNTs/EP was increased by 106.16%, and the nonlinear coefficient is as high as 5.32. In addition, with the increase in PANI doping amount, the nonlinear coefficient of PANI-MWCNTs/EP gradually increases, and the breakdown strength also gradually increases. It can be seen that doping PANI can improve the breakdown strength while maintaining the range of resistivity variation within the nonlinear material working field strength. This discovery can provide reference for the development of nonlinear anti-corona materials for subsequent high-voltage generators.