Ayyoub Zouaghi

Les convoyeurs électrostatiques à ondes progressives (COP) et stationnaires (COS) se présentent comme des moyens avantageux pour manipuler et transporter efficacement des particules sur une surface. L’objectif de cette thèse est d’étudier le comportement de particules diélectriques micrométriques sur ces systèmes. Les études expérimentales commencent par la caractérisation granulométrique et optique des particules et l’analyse de leur charge. Ensuite, l’efficacité de déplacement des particules par les deux types de convoyeurs est étudiée dans différentes conditions. Par ailleurs, les trajectoires des particules sont visualisées en utilisant une caméra ultra rapide. Un post-traitement des images obtenues en utilisant la vélocimétrie par suivi de particules (PTV) est mené pour calculer et étudier la vitesse des particules en fonction de différents paramètres. Les études théoriques et numériques menées avaient pour objectif d’étudier les ondes du potentiel électrique, la variation spatio-temporelle du champ électrique, et le bilan des forces mises en jeu. La dernière partie concerne la modélisation des trajectoires et le calcul numérique de la vitesse moyenne, ainsi que de la distance de déplacement des particules. Les résultats obtenus par modélisation sont en accord avec les observations et les calculs expérimentaux. Plusieurs modes de mouvement sont obtenus en fonction de la fréquence, la tension, la charge et la taille des particules. Les particules sont transportées plus efficacement dans le COP lorsqu’elles sont en mode synchrone sautillant. L’augmentation du nombre de phases permet à la fois de minimiser l’effet des ondes harmoniques inverses et d’augmenter la vitesse de propagation de l’onde directe ; cela mène à un déplacement plus rapide et plus loin des particules dans une seule direction, ce qui augmente l’efficacité du système.

This work investigates the viability of natural and synthetic ester liquids as potential alternatives to mineral oil in MVDC and HVDC transformer insulation systems. Finite Element Method simulations (FEM) were performed using the measured dielectric properties of the oils and their impregnated pressboards as input parameters to evaluate their influence on steady state electric field distribution. A comparison on the field distribution under AC and DC condition is performed for the different materials, identifying regions of maximum stress around the corona head and high voltage electrode. The temperature dependence of electrical conductivity values of the materials and their effect on the steady state DC electric field distribution is explored. The higher conductivity of ester liquids when compared to mineral oil provides a more uniform field redistribution between the oil and pressboard, also facilitating the shift of maximum electrical stress from the oil to pressboard. The results support the technical merits of using ester-based insulation material for field stress equalization in HVDC networks.

The use of high voltage direct current (HVDC) transmission technology has increased significantly in recent years due to its numerous advantages over traditional alternating current (AC) transmission. The aim of the present work is to investigate the efficiency of different non-intrusive sensors for partial discharge measurement in medium or high voltage direct current equipment such as air or gas insulated switchgear. In HVAC systems, partial discharge detection and quantification are well understood. However, under HVDC, it is a necessary to evaluate the efficiency of classic techniques and commercial non-intrusive sensors. This work presents a study of three different sensors for partial discharge measurement under HVDC: high frequency current transformer (HFCT), ultra-high frequency antenna (UHF), and transient earth voltage (TEV). The signals of the different sensors for corona and surface discharge detection are presented and compared in both temporal and frequency domains. The Pulse Sequence Analysis (PSA) technique is used for apparent charge and repetition rate study and the effect of the discharge type on the PSA patterns is investigated. The results show that the PSA patterns are sensitive to the discharge type and conditions. The increase of the applied voltage of corona leads to the increase of the apparent charge differences and the time duration between successive pulses. The spectrums of the discharge pulses of the three sensors are different and the maxima of the TEV and UHF PD signals are dependent on the apparent charge.

The potential of solar energy as a sustainable power source remains hindered by various efficiency limitations. One of the major challenges is the accumulation of dust on photovoltaic (PV) panels, leading to the decrease of the efficiency and the need for regular cleaning. To address this issue, this work aims to explore the use of ionic wind, generated by corona discharge, as an innovative method for dust removal from PV panels. In line with this objective, this paper presents a numerical analysis of electro-hydrodynamic (EHD) air blowers with wire-to-rectangle configurations to harness the potential of ionic wind for cleaning PV panels. The study utilizes 2D models that have undergone experimental validation. The results highlight a parametric analysis, shedding light on how different geometrical parameters influence the performance of the ionic wind air blower and its energetic efficiency.

The potential of solar energy as a sustainable power source remains hindered by various efficiency limitations. One of the major challenges is the accumulation of dust on photovoltaic (PV) panels, leading to the decrease of the efficiency and the need for regular cleaning. To address this issue, this work aims to explore the use of ionic wind, generated by corona discharge, as an innovative method for dust removal from PV panels. In line with this objective, this paper presents a numerical analysis of electro-hydrodynamic (EHD) air blowers with wire-to-rectangle configurations to harness the potential of ionic wind for cleaning PV panels. The study utilizes 2D models that have undergone experimental validation. The results highlight a parametric analysis, shedding light on how different geometrical parameters influence the performance of the air blowers.

Fast and very fast transient overvoltages generally appear during switching operations within electrical substations. The oscillatory nature of such phenomena with frequencies that can reach several tens of megahertz tends to degrade the lifetime of high voltage equipment such as bushings and transformers, inducing partial discharges activity or breakdown of the insulation system. According to several case studies, bushings are one of the most sensitive parts to such overvoltages, indeed, a failure in a bushing will in most cases lead to a failure of the transformer, often catastrophically. Generating such overvoltages with a very high frequency character and considerable amplitude can be very difficult, moreover, studying the effect of such overvoltages on the insulated bushings is not easy, even experimentally. Therefore, a simulation of the fast transients in the system can be very useful to understand the consequences of such phenomena. In this context, this document aims to propose a model of high voltage capacitive graded oil impregnated paper (OIP) bushing based on a distributed electrical circuit. The equivalent circuit is constructed based on the geometric design and electrical properties of the materials. The model was developed and implemented using Matlab/Simulink® software, and was validated with experimental measurements based on impedance sweep frequency analysis. The modeling results are in a good agreement with the experimental ones.

High-voltage direct current (HVDC) links are starting to become widely implemented thanks to their interesting advantages such as reduced operation losses, the absence of reactive power, which allows energy transport via underground cables over long distances, and improved power control. The latter advantage is very essential for renewable energy resource integration into power grids. However, a thorough understanding of the behavior of insulation systems for HVDC components is critical so as to ensure a more reliable service. Indeed, the existence of the direct current (DC) voltage in HVDC components may induce surface and space charge accumulation that can stress insulation further or even promote discharge inception and propagation. As such, this work focuses on showcasing the effect of surface charge on streamers that develop on the interface of liquid–solid insulation due to the advent of lightning impulse (LI) voltage in the HVDC link. This study was performed using finite-element-based numerical simulations that include a quasi-electrostatic model for surface charge accumulation and an electrohydrodynamic fluid model for streamer initiation and propagation. The geometry used was point–plane configuration where the high voltage is applied to the needle electrode located above the liquid–solid interface. The obtained results suggest that streamer initiation is affected by both the accumulated surface charge density and polarity. For a positive streamer, an accumulation of positive surface charge increases the discharge inception voltage as a result of a weakening in the electric field, while an accumulation of negative surface charge decreases the discharge inception voltage due to an intensification in the electric field. Moreover, streamer travel distance and velocity are also both shown to be affected by surface charge accumulation.