Effect of the size of hexagonal boron nitride on the electrical properties of synthetic ester insulating oils

Synthetic ester insulating oils have a high kinematic viscosity and dielectric dissipation factor, making it less likely that heat will be transferred during actual operation. The two-dimensional material hexagonal boron nitride (h-BN) has excellent insulating and heat dissipating properties, which can be added to the insulating oil to improve the electrical properties of the insulating oil. In this study, the isolated hexagonal boron nitride was first characterized morphologically and structurally using scanning electron microscopy, X-ray diffraction, X-ray photoelectron spectroscopy, and UV-visible spectroscopy. Subsequently, the hexagonal boron nitride was added to the pentaerythritol ester oil. Its dispersion stability was first analyzed by determining its size distribution and zeta potential magnitude using dynamic light scattering. Then, the effects of different sizes of hexagonal boron nitride on the dielectric properties and breakdown voltage of the ester oil were evaluated. The results showed that h-BN with a size diameter of 2 μm was more effective in reducing the dielectric dissipation factor to 25% and increasing the volume resistivity by 155% when added at a concentration of 0.01 wt% compared to the base oil. In contrast, h-BN with a size diameter of 0.6 μm at 0.005 wt% significantly increased the average AC breakdown voltage from 66.7 kV in the untreated oil to 79.4 kV. For further insights, dipole moment and electrostatic potential analyses were employed, which showed that h-BN particle size and surface bonding affected the electrical properties of the ester solution.