Influence of ageing on dielectric characteristics of silicone dioxide, tin oxide and ferro nanofluids based mineral oil

Traditionally mineral oil is employed in power transformer as a cooling medium and as an electrical insulator. Recently, massive research work has been carried out to improve the thermal and dielectric characteristics of mineral oil; nanofluids, i.e. nanoparticle-based liquid insulation, seem a feasible alternative. However, concerns have been raised about the dielectric withstand performance of nanofluids after ageing. In this work, an investigation has been carried out to analyze the thermal ageing performance of nanofluids based on silicone dioxide, tin oxide and ferrofluid along with mineral oil. Based on previous results, the selected nanofluids concentration is 0.2 g/l in all tests, i.e., the concentration that allowed to achieve the best dielectric withstand characteristics. To characterize the dielectric withstand properties of the different fluids, we measured the Breakdown Voltage (BDV) and Partial Discharge Inception Voltage (PDIV) of test samples for AC, DC positive and negative voltage. The results illustrate that, under AC voltages, aged nano fluids shows better performance than the base oil (Shell Diala D). In particular, the nanofluid based on silicone dioxide (SO) shows the best performance. The results reported here seems to confirm the applicability of nanofluids in power transformers.