Simulation And Experiment Research On Electrical Arc And Its Extinguishing Methods In Aerospace Relay

Aerospace relay is a hermetically sealed relay with high requirements on life and reliability, and its life depends greatly on electrical arc characteristics and contacts erosion rate during the opening process. A three-dimensional Magneto Hydrodynamic (MHD) model of electrical arc with the existence of required thermal and dynamic environment in aerospace equipments was proposed. The influence of opening conditions on temperature, voltage, arc duration and silver contact erosion of opening arc in nitrogen, hydrogen and helium gases was investigated. Comparison was also made on the erosion mass under different extinguishing methods usable in aerospace relay. The results of this dissertation will provide theoretical basis for designing a long life aerospace relay in future.Thermal dynamic properties and transport coefficients of plasmas formed by gas and contact vapor are preconditions for studying arc characteristics and erosion mass. An empirical approximation method was proposed for calculating the collision integrals between species of silver vapor and species of arcing gases. The Lennard-Jones potential was used to approach interactions between atomic silver and neutral species, and their interaction parameters were obtained through using a combination method. The polarization potential was used to approach interactions between atomic silver and ions produced by gases and between ionized silver and neutral species produced by gases. Finally, minimization of Gibbs free energy and Chapman-Enskog method were used to calculate compositions and thermal physical properties of silver-nitrogen plasmas, silver-hydrogen plasmas and silver-helium plasmas with different silver percentages, in the temperature range of 200 K~20000 K .A three-dimensional MHD model of silver-nitrogen arc was proposed with the thermal and dynamic environments. Silver contact erosion, silver concentration and one-dimensional sheath model were taken into consideration in this model. The modeling method of thermal and dynamic environment was also proposed, where the thermal environment was treated as temperature boundary, pressure boundary and variation in thermal physical properties of arc, and the dynamic environment was treated as body force in the fluid. A dynamic layering method was used to update the calculated meshes during the opening process. The influence of opening factors on arc voltage, arc duration and silver contact erosion was investigated based on this model, and the effect of environments on those arc characteristics was also revealed.Arc extinguishing methods adoptable in aerospace relay were then investigated on the basis of the arc MHD model. The adoptable methods are taking hydrogen and helium as arcing gases, increasing gas pressure, and driving arc by using transverse magnetic fields or radial magnetic fields. It revealed that hydrogen is a promising arcing gas for highest arc voltage and lowest erosion mass, that higher pressure is good for increasing arc voltage and alleviating erosion, and that magnetic fields are also able to shorten the arc duration and alleviating erosion.Finally, an experiment system was realized with the mechanism of collision breaking, which ensured a constant opening velocity. In this system, a high-speed camera was used to take photos of arc imaging and silver concentration during the opening process, and an image processing methods was proposed to extra arc root motion characteristics. Experiments on arc characteristics and erosion mass during the opening process were carried out under different currents, opening velocities and magnetic fields, which proved the validation of simulation results. Good agreements were seen between the simulation arc voltage, arc duration, and arc motion characteristics and their test results, respectively.