Dielectric and thermal characteristics of vegetable oil filled with BN nanoparticles

Vegetable oil, based on natural ester oil, is considered as the alternate natural source of traditional mineral insulating oil in electrical transformers and performs dual functions of insulating and cooling materials. The purpose of this paper is to obtain a new type of nano-modified vegetable oil with both improved electrical and thermal properties. Boron nitride (BN) nanoparticles with high thermal conductivity were dispersed into vegetable oil to form the nanooil. Properties of the oil before and after modification were measured. Thermal conductivity and thermal diffusivity of the nanooil under different temperature were measured to evaluate the influence of BN nanoparticles and temperature on thermal property. Temperature change and heat distribution of the samples in heating process were measured by a temperature sensor and an infrared thermal imager in addition. The thermal bridge, linking the nanoparticle and the bulk liquid, is to contribute to the improvement of the thermal property. Experiments of dielectric property including relative permittivity, dissipation factor and electrical conductivity in a range of temperature were conducted along with the breakdown strength. It is proposed that interfacial region caused by the nanoparticles also contributes to the enhancement of dielectric strength. The trap level distribution of the modified oil, obtained by modified isothermal discharge current (MIDC) test, indicates that the addition of BN nanoparticles affects the trap depth of the vegetable oil and performs influence on the dielectric property and breakdown behavior.