Ablation Controlled Arcs

An experimental and theoretical study on ablation controlled arcs in cylindrical tubes is presented. Measuring techniques for stagnation pressure, electric field strength, mass ablation rate, and arc cross section are described with which a comprehensive set of experimental data is obtained for blackened PTFE as a reference material. These data are interpreted with an isothermal two-zone model that consistently accounts for the balance of mass and axial momentum and yields simple scaling laws for the arc characteristics. Consistent agreement with the experimental data is found for an arc temperature TA = 19 000 ± 2000 K, a vapor layer temperature Tv = 3400 ± 200 K, and a transparently radiated fraction of the arc power of v = 0.32 ± 0.03. The vapor temperature can be explained with a photoablation mechanism. The ablation arc model allows quantifying of the phenomena related to nozzle clogging in gas-blast circuit breakers, namely flow blocking and reverse flow heating. How these phenomena determine the pressure rise in self-blast circuit breakers is shown.