The work presents a comprehensive study of thermal plasma of electric arc discharge between composite electrodes of compositions Mo-50Cu-2Al2O3, Mo-50Cu-2Y2O3 and Mo-50Cu-5Y2O3 (in wt.%). The experiments were carried out in an argon flow at atmospheric pressure and a current of 3.5 A. A combination of spatially resolved synchronized optical emission spectroscopy and laser absorption spectroscopy methods was used to diagnose plasma parameters. The radial distributions of the excitation temperature and the number densities of copper and molybdenum atoms were determined using the Boltzmann plot technique. Based on the experimentally determined plasma parameters, the equilibrium plasma composition was calculated taking into account the dissociation and ionization products of oxide additives, in particular stable monoxides YO and AlO.
Dielectric behaviour of g3 or CO2/O2 mixtures after current interruption have been studied by numerical model. Arc properties during the arcing phase were determined from two-dimensional axisymmetric time-dependent magneto-hydrodynamic simulations. The probability of arc re-ignition (breakdown) after current interruption have been then estimated from evaluation of streamer criterion for the whole calculation domain. Corresponding input data - critical electric fields and effective ionisation coefficients - have been determined from the solution of kinetic Boltzmann equation for the electrons.
For several years now, the gradual electrification of aircraft has been one of the levers for the transition in the aeronautical field. Of course, the all-electric aircraft remains a prospect that does not apply to commercial aviation, but the more electric aircraft, and even hybridisation, seem to constitute concrete developments. Under these conditions, an increase in the electrical power of on-board grids seems inevitable. Future voltages are likely to be +/- 270 VDC or more. Such a change entails new constraints, including the need to switch off DC grids at such voltages and, moreover, at sub-atmospheric pressures. In this article, we present experimental work concerning the opening (at DC voltage) of a contact under aeronautical pressure conditions. The experimental conditions are as follows: pressure is between 200 hPa and 1000 hPa, supply voltage is 540 VDC, and the current when the contact is closed is 50 A. The change in contact voltage and current are measured. The influence of pressure on these signals and on the arc structure observed in fast cinematography is presented.
Ultra-fast opening mechanical switches are proposed as key components for medium-voltage DC circuit breakers, enabling rapid fault current commutation to a parallel capacitor. After arc extinction in the commutating switch, the gas-filled gap is exposed to rapidly rising transient voltages, and the success of commutation depends on fast dielectric recovery. This paper presents a method to estimate the arc temperature at the time of arc extinction and its subsequent decay after full current interruption in a fast-elongating arc with short arcing times. A modified Lowke model, accounting for arc thermal inertia, is used to track the evolution of arc temperature and radius from arc initiation up to arc extinction. Post-extinction gas temperature decay is modeled using heat transfer in a simplified cylindrical geometry. Finally, the dielectric breakdown voltage of the gap is estimated via critical field theory, accounting for temperature-dependent breakdown fields.
To meet the decarbonization objectives set forth by the European Union, the aerospace sector is engaged in the development of a novel category of regional hybrid aircraft that integrates advanced DC technologies alongside conventional systems. This publication presents the proposed direct current (DC) system of the next-generation hybrid aircraft focusing on one of the protection elements developed for the kilo-volt DC (KHVDC) network, namely a mechanical contactor. The contactor design, its key characteristics as well as the chosen numerical model are presented and discussed in detail. The magnetohydrodynamics (MHD) model, details and focuses on a solution that integrates two distinct Ansys software packages, Fluent and Electronics Desktop (Maxwell 3D), chosen to enhance the electric arc modeling in non-linear magnetic environments. The qualitative results obtained from the numerical model will be discussed against experimental observations.
