Statistical Analysis of Natural Ester based Insulating Liquid using 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 are dispersed in the base fluid to formulate the NFs. The assessment of the dielectric behaviour of the insulating liquids is studied for all the varieties of oils-NEO, NEO-NF, aged NEO and aged NEO-NF. The oil samples are 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 is 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 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.