Numerical analysis of local hot-spot temperatures in transformer windings by using alternative dielectric fluids

This paper deals with the thermal characteristics of traditional mineral oil and alternative dielectric fluids. Candidates of alternative dielectric fluids used in the transformer were silicon oil, HMWH, synthetic ester and natural ester. In this study, the transformer which uses synthetic ester and natural ester was focused. 3 ph, 66 kV, 16.5 MVA power transformer and 3 ph, 22 kV, 2.3 MVA distribution transformer were considered and compared the hot-spot temperatures and top oil temperatures by using the computational fluid dynamics (CFD). Kinematic viscosities of natural ester and synthetic ester were four times and three times higher than the mineral oil at the working temperature of respectively. The flow rate of natural ester and synthetic ester was 50-40 % decreased. Therefore, the hot-spot temperature of natural ester and synthetic ester was 24 and 14 % higher than the use of mineral oil respectively.