Christian Fievet

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.

Hydrodynamic Model for Electrical Arc Modeling

A hydrodynamic model for electrical arc modelling is presented. The model, which takes into account Joule heating, radiation, Laplace forces, arc-wall interactions and real gas effect, has been validated through comparisons with measurements. Industrial applications have already been computed and concern high, medium and low voltage circuit breakers.

Hydrodynamic model for electrical arc modelling [in circuit breakers]

A hydrodynamic model for electrical arc modelling is presented. The model, which takes into account Joule heating, radiation, Laplace forces, arc-wall interactions and real gas effect, has been validated through comparisons with measurements. Industrial applications have already been computed and concern high, medium and low voltage circuit breakers.

Theoretical and experimental analyses of the synergism in the dielectric strength for C3F8∕C2HF5 mixtures

Two theoretical approaches are applied in order to describe the behavior of the experimental breakdown voltage in C3F8∕C2HF5 mixtures. First, available cross section data of the electron-molecule processes are scaled to simulate the dielectric strength (DS) behavior in both C3F8 and C2HF5 gases at the level of the Boltzmann equation (BE) solution corresponding to a homogeneous electric field model. Then, the DS of C3F8∕C2HF5 mixtures is evaluated and compared to the experimental breakdown voltage measured using different electrode geometries as sphere/plane type via experimental techniques, i.e., power frequency and negative or positive polarity lightning impulse. Due to the limitation of the BE approach to describe the observed experimental data, the Hunter-Christophorou [J. Appl. Phys. 57, 4377 (1985)] model regarding the positive synergism phenomenon is finally applied. Both models allow us to compare relative values of the “chemical” and “physical” DS components in C3F8∕C2HF5 mixtures.

Determination of copper concentration in a SF/sub 6/ arc plasma in an electrical circuit breaker

Summary form only given, as follows. Measurements of particle temperatures and concentrations were performed for a transient and unstable plasma arc in an industrial circuit breaker operated in a 3 atm SF/sub 6/ gas. The large current intensity caused an important vaporization of the electrodes so that the plasma developed in a mixture of SF/sub 6/ and Cu. Time resolved photographs of the are obtained with interference filters showed a compact and homogeneous zone dominated by a S/sup +/-F plasma, and an inhomogeneous zone close to the electrodes dominated by Cu. Average electron densities and temperatures and also the total number of the different emitting atoms or ions were determined in the two zones by spectroscopy using simultaneous time resolved measurements at high and low spectral resolution. Particle concentrations were obtained after an estimate of the volumes of the different plasma zones by spectroscopical methods. Copper density was also inferred from absorption measurements on copper resonance lines by means of a bright flash produced by a Z-pinch discharge. This method allowed to overcome the problem of light beam random deviation by the strong turbulence in the plasma chamber.

Experimental study of back commutation in low voltage circuit breaker

Summary form only given. During the interuption of a short circuit current with a circuit breaker, an arc is formed in order to eliminate the energy stored in the electrical network. When the operation is performed by a miniature circuit breaker, the arc moved from an ignition area towards a quenching area. In some cases, a phenomenon of arc re-ignition outside the quenching area and far from it (several centimeters) may occur. The so-called back commutation increases the interruption time and the energy expended in the breaker and as a result restricts its efficiency. Our works deal with the study of the arc restrike mechanism. A model breaker has been designed to generate arc restrikes in the ignition area under well known conditions. Typical breaking time and peak current intensity are respectively 10 ms and 5 kA. The set up enables the diagnostic evaluation of very small current (down to several tens of amps) in the limited critical region where the arc restrikes, owing to a novel high sensitivity current measurement device.