Modification Effect of TiO<sub>2</sub> Hollow Nanoparticles on Insulating Properties of Transformer Oil

Abstract

With the promoting of transmission voltage level and the continuous fluctuation of operating conditions by connecting renewable energy into the power system, more stringent requirements have been placed on the operation reliability of transformers and other large electrical equipment. Transformer oil, as the main liquid insulating medium in large power equipment, the modification of its insulating performance has always been research focus in dielectric field. Studies have proved that TiO₂ nanomaterials can not only enhance the AC and positive impulse breakdown voltage of transformer oil, but also significantly improve the aging resistance of transformer oil. However, the DC breakdown voltage of transformer oil has not been greatly increased yet, and sometime even weakened. In this paper, TiO₂ hollow nanoparticles were prepared by hard template method to modify transformer oil. AC and DC breakdown voltage and dielectric permittivity of transformer oil before and after modification were measured and analyzed. The results show that the AC breakdown voltage of the transformer oil can be increased by 32.5%. DC breakdown voltage was increased first and then reduced with the increasing of nanoparticle concentration, while no obvious improvemnet was observed. Based on breakdown mechanism and permittivity of transformer oil, we think the hollow structure of the nanoparticles can significantly enlarge the interface between particle and oil, which greatly promotes the capturing capability to fast electrons and inhibit their migration in the oil, so the AC breakdown voltage are significantly increased. Under DC stress, nanoparticles can capture electrons and meanwhile migrate along fixed direction, which increased electrical conductivity of oil and resulted in lowering of DC breakdown voltage with the increase of nanoparticle concentration.