This presentation was made at the 2019 NAFEMS World Congress in Quebec Canada

Resource Abstract

Mechanical circuit breakers for high voltage direct current networks have been an important and challenging research topic for experimental studies. The main element of such breakers is an axially-blown electrical arc in a convergent-divergent nozzle. Previous work focused on experimental setup and data analysis involving quantities that are difficult or impossible to measure.



This paper provides numerical results that were not accessible in experimental studies. The numerical simulations have been conducted on the original experimental setup using a magnetohydrodynamic framework. We present an analysis of the energy transfer modes of the axially-blown arc under consideration, discriminating between radiative heat transfer and convection. We see that the largest amount of electrical energy is dissipated to the gas flow and removed from the nozzle geometry convectively, and a notable energy fraction is due to radiative heat flux onto the nozzle wall. With respect to the electrical arc, we see that radiative energy transfer is dominant.



Moreover, we show that the electric field along the nozzle axis is larger in the convergent section than in the divergent section because convective cooling leads to a constricted arc shape, and the electric field is locally enhanced at the throat. Comparing electric field values predicted by experiments using a differential method and our numerical simulation results, we show discrepancies between the two methods and provide data for further evaluation of the experimental method.



Although neglecting effects of wall ablation and electrode erosion, the presented results allow for a more complete view on the previous experimental research work, especially on the gas flow field and shock fronts. They also pave the way for further numerical analysis and comparison to experimental data of the geometric layout, and contribute to future developments aimed to more powerful circuit breaker designs.