Streaming Electrification of C60 Fullerene Doped Insulating Liquids for Power Transformers Applications

Long-term and fault-free operation of power transformers depends on the electrical strength of the insulation system and effective heat dissipation. Forced circulation of the insulating liquid is used to increase the cooling capacity. A negative effect of such a solution is the creation of the phenomenon of streaming electrification, which in unfavorable conditions may lead to damage to the insulating system of the transformer. This paper presents results of research confirming the possibility of using fullerene C60 to reduce the phenomenon of streaming electrification generated by the flow of liquid dielectrics. The volume charge density qw was used as a material indicator to determine the electrostatic charging tendency (ECT) of nanofluids. This parameter was determined from the Abedian-Sonin electrification model on the basis of electrification current measurements and selected physicochemical and electrical properties of the liquid. The electrification current was measured in a flow system with an aluminum pipe of 4 mm diameter and 400 mm length. All measurements were carried out at a temperature of 20 °C. The influence of flow velocity (from 0.34 m/s to 1.75 m/s) and C60 concentration (25 mg/L, 50 mg/L, 100 mg/L, 200 mg/L and 350 mg/L) was analyzed on the electrification of fresh and aged Trafo En mineral oil, as well as Midel 1204 natural ester and Midel 7131 synthetic ester. The density, kinematic viscosity, dielectric constant, and conductivity were also determined. A negative effect of the C60 doping on the electrostatic properties of fresh mineral oil was demonstrated. For other liquids, fullerene C60 can be used as an inhibitor of the streaming electrification process. Based on the analysis of the qw parameter, the optimum concentration of C60 (from 100 mg/L to 200 mg/L) resulting in the highest reduction of the electrification phenomenon in nanofluids was identified.