A simple method for estimating mean arc velocities in high-current free-burning arcs is presented. Typical results are presented for arcs burning to copper, graphite and steel cathodes employing experimental values of arc current, electric field, radius and radiation loss. These results are compared with laser-Doppler velocity measurements for the case of copper. The method has also been applied to the studies of Bowman (1972) where a direct comparison with measured velocities has also proved possible and successful. The velocity estimates reveal a number of interesting experimental phenomena. Of particular interest is the implied presence of large velocity gradients in both space and time. The spatial gradients indicate that great care will be necessary in plasma velocimetry techniques based on particle tracking.

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A hydrodynamic model for electrical arc modelling, which takes into account Joule heating, radiation, Lorentz forces, arc - wall interactions and real-gas effects, was applied to study high-, medium- and low-voltage circuit breakers. The first industrial application deals with a high-voltage puffer circuit breaker. Ablation of the nozzle material in this kind of circuit breaker has been studied with the model. The second industrial application presents an self-blast medium-voltage circuit breaker, based on the combination of thermal expansion and the arc-rotation principle. The temperature between the contacts just after the current zero has been evaluated experimentally and numerically. The comparison between these results is discussed. Lastly, the arc commutation in a low-voltage circuit breaker has been simulated. The results show that, in this type of experimental set-up, the interaction among the electrical arc, the flow and the Lorentz force is preponderant.

A sustained current conduction in the breaking chamber after a current interruption has been observed. This current, which we named 'Post-recovery (PR) current', is in phase with the applied voltage and its value ranges from several milliamps up to several amps. The present study shows that the probable origin of the PR current is an ionic conduction of SF6 between the contacts. The estimated temperature of the conducting gas is about approximately 2000 K. The evolution of the temperature is in good accordance with a computational model based on the resolution of two-dimensional Navier-Stokes equations.

This paper is devoted to the study of the phenomenon of arc re-striking in low-voltage circuit breakers. The arc re-strike can be described as a sudden re-appearance in the arcing contact region when the arc had been situated in the quenching chamber a few tens of microseconds before. Our experimental investigations have established that the critical arcing contact region is still crossed by a so-called residual current of the order of several amperes. A gas temperature of around 4000 K was derived both from fine electrical measurements and from a molecular spectroscopy technique just before the occurrence of the arc re-strike. We also demonstrate that the re-strike takes place through the growth of the remaining current of several amperes in the arcing contact region. A numerical approach was carried out with a two-dimensional hydrodynamic code. This was found able to describe the arc movement in the model circuit breaker throughout a high-current-interruption operation and, notably, to simulate the arc re-strikes. The simulation exhibits the role of the flow of gas evaporated from the wall in the process of maintaining a slightly conductive medium in the arc ignition region.