Hocine KHELIFA defended his PhD on Dec. 18th, 2024.
Place : Amphithéatre 203, building W1, ’École Centrale de Lyon (36 Av. Guy de Collongue, 69134 Écully)
Jury :
Rapporteurs :
S. AGNEL, Professeur, Institut d’Electronique du Sud (IES) - GEM, Université de Montpellier, CC079 - Place E. Bataillon - 34095 Montpellier cedex 05
A. HADDAD, Professeur, Cardiff University - United Kingdom
Examinateurs :
J. MARTINEZ, Professeur, Université Paul Sabatier - Laplace - 118 Route de Narbonne - 31062 Toulouse cedex
M-A. RAULET, Maître de Conférences HDR, Laboratoire AMPERE - Université Lyon 1
Encadrement :
E. VAGNON, Maître de Conférences, Laboratoire AMPERE - Ecole Centrale de Lyon
A. BEROUAL, Professeur, Laboratoire AMPERE - Ecole Centrale de Lyon
Abstract :
This thesis explores developing, preparing, and characterizing nanofluids (NFs) to enhance the dielectric performance of insulation liquids commonly used in power transformers, including synthetic esters, natural esters, and mineral oils by incorporating different types of nanoparticles (NPs). These later being conducting (Fe3O4, C60, Gr), semi-conducting (ZnO and CuO), and insulating (Al2O3, ZrO2, SiO2, and MgO). The study aims to improve dielectric properties, including the AC breakdown voltage, partial discharge (PD) resistance, electrostatic charging tendency, and surface discharge characteristics. A comprehensive analysis covering the historical evolution, preparation techniques (one-step and two-step methods), and stabilization mechanisms essential for achieving stable nanofluids with optimal dielectric properties is presented. The preparation protocols of NFs, as well as the various experimental set-ups and methods used to characterize them dielectrically, are then described. The impact of NP characteristics, such as the type, size, concentration, and surface treatment, on the dielectric performance of base liquids is systematically assessed. The experimental data are then analyzed using statistical tools such as the Anderson-Darling goodness-of-fit test and Weibull probability analysis, and the voltages corresponding to 1%, 10%, and 50% risk levels were determined. The involved mechanisms in the improvement/deterioration of AC breakdown voltage are discussed. The experimental results indicate that nanofluids (NFs) significantly enhance the dielectric properties by reducing partial discharge activity, the electrostatic charging tendency, and the stopping length of surface discharges. This improvement is achieved by influencing charge mobility within the liquids. Both conducting and insulating nanoparticles (NPs), particularly Fe3O4 and Al2O3, demonstrate substantial benefits, which can help mitigate breakdown events and extend equipment longevity. Additionally, the interaction of nanoparticles at solid-liquid interfaces affects surface discharge behaviors, further supporting the role of nanofluids in enhancing insulation durability.
Keywords: Nanofluids, Transformers oils, Metal Oxides Nanoparticles, Carbonic Nanoparticles, dielectric Properties.