Laboratoire de Mécanique des Fluides et d'Acoustique - UMR 5509

LMFA - UMR 5509
Laboratoire de Mécanique des Fluides et d’Acoustique
Lyon
France


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Accueil > Actualités > Thèses - Habilitations à diriger des recherches

Soutenance de thèse ECL

Paolo Errante

Mercredi 5 février 2020, 14h, amphi 1, bât. W, ECL

Paolo Errante

Liquid spray injection in the expansion volume of a CO2 high voltage circuit breaker

Composition du jury
Tonini Simona, Professeur, Université de Bergame (Italie), Rapporteur
Hoarau Yannick, Professeur, Université de Strasbourg, Rapporteur
Matas Jean-Philippe, Professeur, Université Claude Bernard Lyon I, Examinateur
Freton Pierre, Professeur, Université Toulouse 3 - Paul Sabatier, Examinateur
Corre Christophe, Professeur, Ecole Centrale de Lyon, Directeur de thèse
Makhlouf Samir, Docteur-ingénieur, SuperGrid Institute, Encadrant

Résumé

Electric networks represent one of the key element of industrialized societies wellness. Their main role is to bring connection between electric power production and consumption sites, providing well specified standards of quality, safety and security. Atmospheric phenomenons such as rainfall, lightning strikes and strong winds may provoke severe accidents to the electricity transport equipment, leading to service deficiencies. To protect the electricity transport infrastructure from such anomalies, the interruption of faults currents is required. This task is assigned to devices known as circuit breakers.
In these kind of switchgears, the mechanical disconnection of elecricity conductors parts is realized to interrupt the current passage. The electrical breakdown of the medium in which such contacts are immersed, occurs when the voltage is sufficiently high.
The generation of an electric arc causes the current to flow between the two contacts. Specific measures have to be adopted in order to confine and extinguish the electric arc, for a definitive interruption of the current passage. Nowadays, in AC transmission grids, the fault current interrupting technologies are based on the use of the SF6 (sulfur hexafluoride). SF6 is harmful for the environment because of its high Global Warming Potential. Ongoing researches within SuperGrid Institute aim at proposing alternative interruption technologies not using SF6.
Unfortunately, replacing SF6 with environment friendly gases worsens the current interruption process : their physical properties being not sufficient to ensure the same performances observed when SF6 is employed. A possible way to overcome this limitation is to enhance clean gases properties by adding some chemical species. In the framework of the research activities of the High Voltage Substation Equipment program of SuperGrid, it has been proposed to introduce such species by mean of an evaporative liquid spray.
Inside the expansion chamber of the circuit breaker, a liquid jet is atomized so to form a droplets cloud. The liquid droplets, due to the interaction with the hot gases surrounding the arcing zone, evaporate. This causes the release of chemical species which joins the gas phase to modify its physical properties. This Ph.D thesis work cames as a complementary activity to the experimental investigations performed at SuperGrid institute. The main objective is to better understand, by mean of a numerical model, the most meaningful flow features occurring during the current interruption process. To understand how the liquid spray interacts with the gas phase and the entity of the vapor released to form the desired gas mixture, the first task is to bring together several modeling ingredients to build a numerical methodology.
An Eulerian-Lagrangian approach is chosen to capture some of the phenomenons occurring when a liquid spray injection is performed inside the circuit breaker. The electric-arc causes the insulating gas to undergo severe temperature and pressure conditions. To correctly describe the fluid thermodynamic and transports properties in such circumstances, specific choices have been required. The models results are discussed and used to investigate the eventual margins of improvement of the novel design of circuit breaker.

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