Numerical Research on Cooling Performance of Magnetic Nanofluids in a Natural Convection Transformer

The transformer is extensively cooled internally by natural convection, which can handle most electrical load conditions and ensure that the maximum internal temperature (hot spot temperature) does not exceed the allowable value. However, sometimes the variable load operation of the transformer causes its temperature rise, which will reduce its service life and may cause thermal failure. The purpose of this paper is to enhance the cooling performance of transformer with ferrofluids. Different from transformer oil, ferrofluids have higher thermal conductivity and are subject to magnetic force under the action of temperature and magnetic field gradient. Therefore, a two-dimensional axisymmetric single-phase transformer cooled by natural convection with oil-based ferrofluid is numerically studied and compared with that by transformer oil. The results show that the thermomagnetic convection is formed at the upper and lower angles of the transformer core, weakening the hot plume generated by natural convection. Vortices have also appeared in the lower part of the oil tank. The heat transfer state in the region depends on the relative magnitude of thermal-magnetic convection versus natural convection, with the addition of thermal-magnetic convection enhancing natural convective heat transfer. The hot spot temperature in the coil has decreased from 73.4 °C to a maximum of 67.5 °C.