Effects of viscosity of ester oils and different sizes of suspended cellulose particles on bridging phenomenon under non-uniform DC electric field

Petroleum-based mineral oils are insulating media that are typically used in the industry, particularly for high voltage (HV) applications. In recent years, however, there is growing interest among researchers to formulate novel dielectric liquids in replacement of petroleum-based mineral oils since mineral oils are non-biodegradable and highly flammable. In addition, the dielectric performance of mineral oils is somewhat limited and therefore, there is a need to develop alternative insulation oils with superior dielectric performance in order to fulfil the demanding requirements of dielectric liquids. One of the promising substitutes for mineral oils is ester oils. In this regard, this research investigates the bridging phenomenon in two types of ester oils with different values of viscosity, i.e. natural and synthetic esters under the influence of direct current (DC) electric field. Three different sizes of contaminants are used, i.e. 100, 300 and 500 μm. The results show that both the size of particles and oil viscosity play important roles in the formation of cellulose bridge and breakdown behaviour.