208 / 2022-03-14 18:58:58

Effect of Fullerene Nanoparticles on the Electrostatic Charging Tendency of Synthetic Ester Midel 7131

fullerene C60,Nanofluid,Electrostatic Charging Tendency (ECT),GIGRE Cell

The static charge that can be generated in power transformers (PT) when the oil flow circulating in the cooling ducts of this device exceeds a critical value, can lead to the failure of this latter. This static charge results of the contact of insulating oil with paper/pressboard during the flow of oil. Thus, the knowledge of the charging tendency (ECT) and its level are of great interest for the manufacturers and users of PT. Numerous studies have been devoted to the ECT of mineral oils and how to reduce the level of static charge. Thus, research carried out in the late 1970s showed that it was possible to reduce ECT by adding certain antistatic additives to the oil such as alkylbenzene, theophiline, and benzotriazole (B.T.A). B.T.A. is also used by some oil companies (especially, Japanese) as an oxidation inhibitor product, slowing down the catalytic effect of copper, thereby reducing the oxidation of oil. Unfortunately, the beneficial effect of B.T.A. is controversial today, as it would only last a few weeks.

This static electrification issue is back on the agenda with the development of new insulating fluids, in particular synthetic ester (SE). This latter has been indeed introduced these last years in some PT worldwide. Thus, it is fundamental to know the ECT of this fluid. Besides, for about twenty years, work has been undertaken to improve the dielectric strength of SE by adding nanoparticles or specific molecules into it; the aim being the improvement of the characteristics of this liquid, especially its dielectric strength and heat transfer.

This work deals with the effect of fullerene nanoparticles (C₆₀) on the electrostatic charging tendency (ECT) of SE, Midel 7131. The investigation will be undergone on a spinning moving disk system (CIGRE Cell) versus the rotating speed of the disk. The method of preparation and treatment of nanofluids (NFs) samples will be described. Then, the long-term stability of the NF sample will be checked considering Zeta potential measurement. After that, a comparison of ECT of pure Midel 7131 and the SE-based fullerene nanofluid with be performed considering various disk speeds ranging from 200 to 700rpm for a concentration of 0.4 g/L. The choice of this concentration is based on our recent experimental results which showed that this nanofluid (SE-based fullerene NF) presents a considerable reduction of partial discharges activity and that this concentration gives the best improvement in the AC breakdown voltage.