Improved electrical resistivity-temperature characteristics of insulating epoxy composites filled with polydopamine-coated ceramic particles with positive temperature coefficient

Incorporating positive temperature coefficient (PTC) ceramic particles into polymer matrices provides a promising solution to suppress the distortion of DC electric field within polymeric insulation caused by the negative temperature coefficient (NTC) of electrical resistivity. However, along with the suppressed NTC effect comes the decrease of dielectric strength due to the agglomeration of PTC particles. Here, we addressed this issue in the epoxy resin system by coating polydopamine onto PTC particles to improve the compatibility with matrix, thus achieving a maintained DC breakdown strength. The improved evenness of PTC particles dispersion also provided sufficient interface to generate interface charge traps, which contributed to the increase of electrical resistivity at elevated temperature. Combined with temperature dependent charge carrier amount affected by PTC filler, NTC effect of epoxy composites was further mitigated and the maximum DC electric field was reduced by 49% within insulation assessed by the simulation of HVDC bushing. The method proposed in this paper is crucially important for the reliable and economic application of composite dielectrics under harsh conditions.