Effect of the Coexistence of Al2O3 Nanoparticles and Water on Transformer Oil Electrical Performance

It has been found that the introduction of nanoparticles (NPs) into transformer oil can alleviate the destructive effect of water on the insulation properties. Researchers have begun to explore the mechanism behind this phenomenon and try to provide possible explanations. However, the effect of water on the electrical properties of NF has not yet been explained definitively due to many factors, such as the NP concentration and external electric field. In this paper, mineral oil-based Al₂O₃ NFs with a wide range of NP concentrations and moisture content are prepared and tested to study the effects of their coexistence on the electrical properties of transformer oil. Diagnostic techniques (including ac breakdown voltage, thermally stimulated current, and dielectric spectroscopy) have been used to measure the dielectric properties of samples with varying relative humidity. The experimental results show that different NP concentrations and relative humidity can obviously affect the electrical performance of transformer oil. The breakdown voltage of the NF significantly improved compared with that of pure oil with the introduction of Al₂O₃ NPs at varying relative humidity. The shallow trap density in NF significantly increases due to the introduction of NPs with different relative humidity. The proper mechanisms of the water forms with different water contents are discussed based on the results of the experiment. The study of the electrical properties of NFs with different relative humidity is a good complement to current studies in this field.