Investigation of natural ester based insulating liquid using statistical hypothesis testing

An important element of the power system network is the transformer. The conventional mineral oil (MO), which acts as an insulation and heat transfer agent in a transformer plays a major role in its steadfast operation. The insulation is highly stressed during its operational lifetime. Thus, alternative insulating liquids are being studied to enhance the reliability of the transformer. This paper furnishes a comparative investigation of the breakdown voltages of natural ester-based insulating oil (NEO) and its nanofluids (NEO-NFs) used in power and distribution transformers. The semi-conductive Titanium oxide (TiO2) nanoparticles (NPs) with a suitable weight percentage were dispersed in the base fluid to formulate the NFs. The assessment of the dielectric behaviour of the insulating liquids was studied for all the varieties of oils-NEO, NEO-NF, aged NEO and aged NEO-NF. The oil samples were aged in an open beaker oxidative ageing (OBOA) apparatus. The AC breakdown voltage (ACBDV) is measured using paired spherical electrodes as per the relevant standard. The hypothesis testing was done to ascertain if the breakdown data for all the oil samples follow a particular probability distribution and a statistical analysis is done. The failure probabilities of 5%, 10% and 50% are considered for the Normal and Weibull distribution functions to analyze the experimental data. It is observed that NEO-NFs performed better than the base fluid in terms of its breakdown value, both before and after ageing process. The goodness of fit analysis is carried out to ascertain which distribution fits the data well. © 2021 The Institute of Electrical Engineers of Japan.