Effect of Magnetic and Non-magnetic Nanoparticles on Insulation and Cooling Behaviour of a Natural Ester for Power Transformers

This paper analyses and compares the impact that maghemite and titania nanoparticles have in the electrical and thermal performance of a commercial natural ester used in power transformers. Vegetal-oil-based nanofluids have been prepared at different concentrations. Once the nanofluids were obtained, the breakdown voltage of the oil samples with and without nanoparticles was measured. It was found that the concentration of nanoparticles influences the breakdown voltage of natural ester. The existence of optimal concentrations has been noticed, and these nanofluids were selected for the upcoming tests. The cooling capacity of these liquids and the base fluid was measured through a thermal analysis in an experimental platform. The experiment developed is based on a 1-phase transformer (800 VA, 230/115 V) immersed in a stainless-steel fulfilled with insulating liquid. The temperatures inside the tank were monitored at the bottom and at the top of the tub to measure the oil temperature. Other sensor measured the hotspot winding temperature, defined as the hottest temperature of winding conductors in contact with solid insulation or insulating liquid. This sensor was located at the top of the winding as the most probable hot-spot location. Ambient temperature was also measured as a reference. A microcontroller (Arduino) and an Integrated Development Environment (IDE) was utilized to record the measurements of the sensors. The results of the thermal study showed that only maghemite based nanofluids exhibited improved heat transfer characteristics in comparison with the natural ester oil.