Pascale Petit

Arc-wall interaction modelling in a low-voltage circuit breaker

A hydrodynamic model for electrical arc modelling is used to study the interaction between the electrical arc and the sidewall in a low-voltage circuit breaker. The interaction model is based on an energy balance at the boundary. Comparisons of pressure, arc voltage and ablated mass between computations and experiments validate the model. The results confirm that the main mechanism at the sidewall is the photo-ablation. The model shows that, very rapidly, plastic vapours replace the air in the circuit breaker and are responsible for a residual conduction in the arc initiation region.

Optical diagnostics and numerical modelling of arc re-strikes in low-voltage circuit breakers

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.

Experimental and numerical studies of arc restrikes in low-voltage circuit breakers

This paper is devoted to the study of the arc restrike phenomenon in low-voltage circuit breakers. We focused our interest on the type of arc restrike that can be described as a sudden reignition in the arcing contact region while the arc was situated in the quenching chamber a few tens of microseconds before it occurs. Our experimental investigations have established that the critical arcing contact region is still crossed by a so called residual current on the order of several amperes. A gas temperature around 4200 K was derived from electrical measurements in this region before the arc restrike occurrence, We also demonstrate that the restrike 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 in order to simulate the gas behavior in the arcing contact region before and during the arc restrike phenomenon. The same temperature as the measured one is calculated just before the restrike. It is demonstrated that the current density appears to be the most sensible quantity. A critical value of 5 A/cm/sup 2/ was calculated.