I. Introduction
To make transformer oil-based nanofluids widely applied in power equipment, the main problem that needs to be solved is the stability of transformer oil-based nanofluids. At present, there are many methods for evaluating the stability of nanofluids, mainly including sedimentation method, absorbance method, particle size analysis method and Zeta potential method. Each method has its own advantages and disadvantages. According to the research object and the observation time, choosing the right measurement method is important for accurately assessing the stability of the nanofluid. In this paper, particle size analysis and UV-vis spectrophotometry were used to comprehensively evaluate the stability of transformer oil-based nanofluids.