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Study on dielectric and discharge characteristics of nano-Al2O3 modified insulating paperboard under AC-DC combined voltage

The oil-paper insulation system on the valve side of the converter transformer works under complex electrical stress for a long time, which are prone to insulation problems. With the current in-depth research on nanocomposite materials, it has become a feasible method to improve the insulation performance of paperboard through nano-modification. In view of the above problems, firstly, modified insulating paperboards containing different concentrations of nano-Al2O3 were prepared, and the changes of parameters such as relative permittivity, volume resistivity and dielectric loss tangent of oil-impregnated paperboard with doping concentration were studied. Subsequently, the breakdown experiments of the modified insulating paperboard under AC and AC-DC combined voltage were carried out. The study shows that the doping of nano-Al2O3 can effectively reduce the relative permittivity and dielectric loss of the insulating paperboard, and improve the volume resistivity of the insulating paperboard to a certain extent. With the increase of the doping ratio of nano-Al2O3 particles, the breakdown strength of the insulating paperboard first increase and then decrease. Finally, the optimal doping concentration under different DC components is obtained. This work is of great significance to the optimization of converter transformer insulation and the application and promotion of modified paperboard under complex electric fields.