Caracterisation et simulation numerique d'un isolant soumis a une tension continue dans un Poste Sous Enveloppe Metallique (PSEM)

National audienc

Phénomènes de conduction dans les gaz et isolants solides compris dans les Postes Sous Enveloppe Métalliques soumis à une tension continue

With the emergence of renewable energy, new technologies for energy distribution across long distances, such as High Voltage Direct Current in Gas Insulated Substations (HVDC GIS) are developed. Under HVDC, the electric field distribution is not anymore determined by permittivity of materials but by resistivities and charge accumulation. In presence of gas/solid interfaces, the role of the surrounding gas on charge accumulation must be considered. In this work, we first present characterization methods which allow measuring the current passing through gas and solid insulators for different environmental conditions. Using these methods, we investigate the influence of several parameters (temperature, electric field, relative humidity) on the measured current. The variations of volume and surface resistivities are obtained. Finally, the results obtained for both solid and gaseous insulations are used to develop a numerical model with a shape close to the industrial application, and observe the modification of electric field distribution in presence of water concentration and temperature gradient in an HVDC GIS.Avec l’émergence des énergies renouvelables, de nouvelles technologies pour la distribution de ces énergies sur de longues distances, telle que les Postes Sous Enveloppes Métalliques (PSEM) soumis à une haute tension continue (HVDC), sont développées. Sous HVDC, la distribution du champ électrique n’est plus déterminée par la permittivité relative des matériaux mais par leurs résistivités et l’accumulation de charge en surface des isolants. En présence d’interfaces gaz/solide, le rôle du gaz environnant sur l’accumulation de charge doit aussi être pris en compte. Dans ce travail de thèse, nous présentons tout d’abord des méthodes de caractérisations permettant de mesurer le courant au travers d’un gaz et dans les isolants solides, pour différentes conditions d’utilisations. Grâce à ces méthodes, nous avons pu étudier l’influence de plusieurs paramètres (la température, le champ électrique, l’humidité relative) sur le courant mesuré. Les variations des résistivités de volume et de surface sont ainsi obtenues. Enfin, les résultats obtenus pour les isolations solides et gazeuses ont été utilisés pour développer un modèle numérique présentant une forme similaire à celle utilisée dans l’application industrielle. Nous avons donc pu observer les modifications de la distribution du champ électrique induites par la présence d’eau et/ou des gradients de températures dans un PSEM sous haute tension continue

Surface Resistance Measurements on Epoxy Composites, Influence of Surrounding Gas, Pressure, Temperature, and Analysis of the Origin of Measured Currents

International audienc

Dark current measurements in pressurized Air, N2 and SF6

International audienc

Surface potential decay of an epoxy resin : influence of material's w ter content, air's relative humidity and temperature

International audienc

Study of Surface Resistivity of an Epoxy/Gas Interface versus Electric Field and Relative Humidity

International audienceSurface resistivity of solid insulators is usuallydetermined by measuring the current induced when an electricfield tangential to the surface is applied. This classical methodcan become questionable when the electric field is raised. In fact,a current may also flow above the interface through the humidgas, in addition to currents flowing at the interface and below theinterface within the solid bulk. This paper presents anexperimental study of the variation of the surface resistivityversus electric field and relative humidity RH of the surroundinggas. The results show that in dry gas (RH < 1%) and for anelectric field up 8 kV/mm, the surface gets no specific propertiescompared to the volume. However, in humid gas (1% < RH <10%), a decrease of the net surface resistivity (by subtracting thecurrent above and below the interface) is detected

Dark current measurements in pressurized SF6: influence of relative humidity and temperature

International audienceCurrent measurements in pressurized gases at high electric field are performed using electrodes with coaxial geometry. To identify the main mechanisms involved in “dark current” measured, the influences of electrode roughness, gas pressure, relative humidity and temperature have been investigated. The experimental results reveal that charge injection from the electrode constitute the main mechanism responsible for dark current. The latter is considerably modified when relative humidity RH is changed via the influence of pressure and temperature. The measured current shows an exponential increase versus electric field and also versus RH. It is thus assumed that water adsorbed on the electrodes induces an enhancement of charge injection from the electrode surface

Dark current in pressurized Air and SF6 versus electric field, pressure, and temperature

International audienc

Dark current measurements in humid SF6:influence of electrode roughness, relativehumidity and pressure

International audienceThe measurement of ‘dark current’ in pressurized SF6 at high electric field is performed usingelectrodes with a coaxial geometry. To identify the main mechanisms involved in measuredcurrents, the influences of electrode roughness, gas pressure and relative humidity have beeninvestigated. The experimental results reveal that charge injection from the electrode constitutethe predominant process responsible for the dark current. The latter is nearly identicalin positive and negative polarities, and shows an exponential increase versus the relativehumidity and the electric field. The analysis of results shows that under high electric field,the emission of charged water clusters from the water films adsorbed on electrodes probablyconstitutes the main mechanism of charge emission

Measurement and analysis of Partial Discharges in HVDC gas insulated substations

International audienceThe measurement of Partial Discharges (PD) in Gas Insulated Substation (GIS) enables to identify and analyse various types of defects that can result in electrical breakdown. Unlike the case of alternative current, the measurement techniques of PD in direct current are less mature and require more investigations for the development of suitable recognition tools; the mechanisms involved in direct current being different from those of alternative current. This paper deals with experimental characterization of a real-size part of a 320 kV GIS filled with various gases (SF6 , N2 , Air), at room temperature and for a pressure range from 0.1 to 0.5 MPa. To characterize the partial discharge signatures of existing defects, a protrusion fixed on high voltage conductor and a free metallic particle are considered. The test are achieved according to IEC 60270 recommendations. The experimental results reveal different regions with characteristic apparent charge distribution and PD pulse frequency. It is also evidenced that the variation of pressure and the voltage polarity influence the succession of regions. Different PD patterns are identified depending on the considered defect and polarity