Research On Dielectric Recovery Characteristic Of Small Capacitive Current In SF₆Circuit Breaker

The breaking performance of circuit breakers depends primarily on the competitionbetween dielectric recovery and the rating of recovery voltage between contacts. Residualarc column still exists in the arc gap after the short period of time of the extinction, whichwill seriously affect the dielectric strength and speed of recovery, moreover, the diffusionof the plasma arc, complex of charged particles and electrons and neutral particle densityare closely related with the dynamic characteristics and flow characteristics of the arc.Therefore, considering the impact of flow characteristics, establish the mathematical modelaccurately is the key to study the dielectric recovery characteristics of circuit breakers afterarcing.This paper establishes a model for the conductivity of non-equilibrium dualtemperature arc plasma during small capacitive current interruption in a SF6circuit breaker.Considering the contributions of electron-ion-neutral particle collision frequency andcollision cross-section, we obtain the conductivity of SF6plasma as a function oftemperature and pressure and establish a dynamic arc model for small capacity currents.Based on the model, a numerical simulation is performed on the flow field with a load ofsmall current for a126kV SF6circuit breaker. Density, pressure and temperaturedistributions inside the circuit breaker chamber are obtained. With the electric field insidethe same interrupter, combining streamer theory breakdown criterion，dielectric recoverycharacteristic curves are described. The calculated results were compared with the resultsunder equilibrium conditions.Based on its actual ablative situation of SF6circuit breaker contacts, establishcalculation model to calculate dielectric recovery characteristics under this case. Compareresults obtained with that under the non-ablative case, analyze the impact of ablation ondielectric recovery characteristics. And then change arcing time to analyze the impact ofarcing time. Considering the extrusive wear of dynamic arcing contact to static arcingcontact, study the effects of different burning conditions on the electric field distribution through the three-dimensional electric field analysis of the interrupter. Based on the aboveanalysis, I proposed ways to improve impact of the contact burning on recoverycharacteristics.Based on the actual prototype opening speed of SF6circuit breakers, adjustment get adifferent opening speed, calculated its conduct flow field under the load.criticalbreakdown voltage curves of arcing contacts after the zero-crossing were obtained.Analyze the impact of velocity changes on its calculation results in the electric field andthe flow field. Change the arcing time, breaking analysis of the different speeds of theshort-time arc arcing recovery characteristics of the medium.