Recent progress in nanofluids based on transformer oil: preparation and electrical insulation properties

Given the adoption of ultrahigh-voltage ac and dc power transmission, it is desirable to develop a new kind of oil-paper insulation system, with higher dielectric strength and smaller volume compared with conventional insulation systems, in order to reduce the volume and mass of high-voltage power transformers and improve their long-term operational reliability [1], [2]. Methods of improving the dielectric properties of the oil-paper insulation have therefore been widely investigated [3], [4]. The most influential factors affecting the performance of oil-paper insulation systems are the low dielectric strength of transformer oil and its degradation caused by water and other contaminants [5]. The dielectric strength of oil-paper insulation may be increased by filtering the oil in order to remove water and other contaminants [6]. However, further increase in the dielectric strength of the oil is required in order to achieve reduction of transformer volume and mass.