This paper is devoted to investigate the effect of a strong external magnetic field on the electric arc created by contact opening in a low-voltage switch. The low-voltage switch is powered by a DC generator with an RL charge as in photovoltaic installations. During contact opening, the arc motion is dominated by Laplace and hydrodynamic forces. An external magnetic field is added to strengthen the magnetic forces and to accelerate the arc extinction. Significant differences depending on the external magnetic field intensity can be investigated. Numerical simulations, developed using COMSOL Multiphysics, are compared to experimental measurements performed on experimental device specially designed for tests to provide a better understanding of the physical phenomena involved.

The paper deals with an experimental investigation of the pressure drops and friction factors induced by sets of metal woven screens in the case of an incompressible fluid flow, namely water flow. These woven screens are of metallic type and are used in electrical safety devices, especially at the end of exhaust duct of low voltage circuit breakers. In a first step, the whole of the set-up is used to check some approximations dedicated to pressure drops due to sphere beds around 275 gm and 375 gm as diameters. Results are discussed in terms of Darcyan and non-Darcyan permeabilities compared with published data and are analyzed in terms of the Blake-type friction factor. In the second step, the pressure drops are measured for stacks composed of eight different woven screens (of plain dutch type) formed with millimetric wires. Various formulations of the pressure drops and friction factors published elsewhere are tested with a special care dedicated to the choice of the geometry for the flow pattern (hydraulic diameter, spherical diameter, cylindrical diameter) and to the consideration of laminar and turbulent contribution. We then give the formulation that characterizes the fluid flowing through stacks of woven screens used in electrical safety applications. (C) 2017 Elsevier Inc. All rights reserved.

During the working of electrical fuses, inside the fuse element the silver ribbon first begins to melt, to vaporize and then a fuse arc appears between the two separated parts of the element. Second, the electrodes are struck and the burn-back phenomenon takes place. Usually,the silver ribbon is enclosed inside a cavity filled with silica sand. During the vaporization of the fuse element, one can consider that the volume is fixed so that the pressure increase appears to reach pressures higher than atmospheric pressure. Thus, in this paper two pressures, 1 atm and 10 atm, are considered. The electrical field inside the plasma can reach high values since the distance between the cathode surface and the anode surface varies with time. That is to say from zero cm to one cm order. So we consider various electrical fields: 10~2V/m, 10~3V/m, 5×10~3V/m,10~4V/m at atmospheric pressure and 10~5V/m at a pressure of 10 atm. This study is made in heavy species temperature range from 2,400 K to 10,000 K. To study the plasma created inside the electric fuse, we first need to determine some characteristics in order to justify some hypotheses.That is to say: are the classical approximations of the thermal plasmas physics justified? In other words: plasma frequency, the ideality of the plasma, the Debye-Hückel approximation and the drift velocity versus thermal velocity. These characteristics and assumptions are discussed and commented on in this paper. Then, an evaluation of non-thermal equilibrium versus considered electrical fields is given. Finally, considering the high mobility of electrons, we evaluate the electrical conductivities.

Low-voltage circuit breakers under critical situations such as a severe short circuit develop a strong electric arc leading to brutal manifestations such as envelope rupture or fire. Apparatus are strictly designed to avoid damages like personal injury and material destruction. To limit the external manifestations of the electric arc, an efficient way consists of inserting a porous filter in the gas exhaust duct, composed of metallic cloth arranged in a Reps structure. Experimental tests have demonstrated the efficiency of this technique. We propose to complete the experimental study by carrying out the numerical simulations about the filter impact on the hot gas flow. A 2-D model based on the gas flow in porous media is considered, taking into account the porosity variation while the electric arc model derives from the experimental data and a thermal radiation model. A sophisticated finite-volume method based on a well-balanced scheme developed for nonconservative system is used to correctly approximate the solution when dealing with porosity variation.

Precedent simulation work determined that Laplace forces could have an effect on the prearc-arc transition in fuses [1-2]. An experimental study on exploding wire is done to understand transition differences between low and high current variations. The paper is focused on the low current variations.

Most of nonconservative hyperbolic systems corresponds to a reduction of an initial three-dimensional problem deriving from a homogenization procedure. Unfortunately, the reduced model gives rise to two new difficulties: the resonance problem corresponding to a splitting or a merging of the genuinely nonlinear waves and the non uniqueness of the Riemann problem solution. The question arises to check whether the two problems correspond and provide similar solutions, at least numerically. In this paper, we propose a comparison between the one-dimensional nonconservative Euler equations modelling the duct with variable cross-sectional area with its original three-dimensional conservative Euler system. Based on the classification of the Riemann problems proposed in [13], we compare the numerical results of the two models for a large series of representative configurations. We also propose a new example of non uniqueness for the Riemann problem involving the resonance phenomena.

Electrical needs are continously growing because of many various factors linked to increasing consumption and a green perception. This development - geographical, increasing production, growth of transport network, interconnection of continental networks, diversity of the transport technologies. - can not be dissociated from electrical safety considerations whatever the voltage level. For the three main levels of electric network - High Voltage, Middle Voltage and Low Voltage - one has to provide efficient electrical safety techniques or schemas which integrate different electrical safety apparatus. Among well-known apparatus we can cite SF6 breakers, HV and MV switchgears (such as MV cells, MV and LV high current vacuum switchgears), and fuses. Electrical fuses are especially used in the MV and LV domains, sometimes as an additional safety device and sometimes as the main electrical safety component which is linked to the electrical current breaking function of electric fuse. In the paper, we will quickly depict the various kinds of electric fuses. We will especially focuss on the physical mechanisms - whatever the type of work, experimental, theoretical, modelling or empirical - prevailing during the pre-arcing period of the electric fuse operation.

In the electric fuse operation the arcing period follows immediately the pre-arcing period depicted in Part 1 (Part 1. Pre-arcing period). The transition between these two operation steps is not fully understood at this time. To simplify the beginning of the arcing period can be identified with the electric arc ignition i.e. with the electrodes voltage drop. The consecutive plasma is of metallic type at the beginning of the arcing period and of metallic plus silica type with varying mixture up to the end of the arcing period. The energy brought by the fault current is withdrawn by means of the interaction between the electric arc and the arc quenching material (usually silica sand) whose morphometric properties influence the properties of the plasma column: composition, thermodynamic properties and transport coefficients of the plasma column depend on the porosity (and other morphometric properties) of the filler. The fuse element erosion also known as burn-back is responsible for the lengthening of the plasma column and the variations of the electric field. The whole of these processes is depicted by means of experimental results or modellings when possible.

The aim of the paper is to test the accuracy of classical spectroscopic methods in the visible domain dedicated to measurements of temperature and electron density in order to conclude about the validity of thermal disequilibrium. The influence of various factors is studied: accuracy of the intensity calibration, Abel inversion of the experimental spectra, excitation temperature deduced from the relative method, absolute excitation temperature, influence of the transition probability accuracy, influence of the Biberman factor value, electron temperature from the line-to-continuum intensity ratio, electron density deduced from Stark broadening, and electron density deduced from the continuum intensity. This spectroscopic investigation is carried out for argon plasma and argon copper plasma both produced by means of an ICP torch operating at atmospheric pressure. Results are given with uncertainties for each evaluated parameter. We show that, first, the electron temperature deduced from the line-to-continuum intensity ratio has to be considered with great care; second, for argon plasma no evidence of thermal disequilibrium can be discerned, whereas for argon copper plasma a small disequilibrium of 1.2 to 1.4 at most is experimentally observed.

La presente invention concerne un procede de fabrication d’un fusible, comprenant une etape de determination de la geometrie d’au moins une lame fusible (16) equipant ce fusible, dans laquelle on considere les parametres suivants : une intensite nominale de conduction (i16) de la lame fusible (16) ; une tension nominale de fonctionnement du fusible ; une integrale de Joule correspondant, en regime pre-arc, a au moins une partie (18) de la lame fusible, et une integrale de Joule correspondant, en regime d’arc, a cette partie (18) de la lame fusible. Le procede est caracterise en ce que, dans cette etape de determination, on considere egalement des forces de Laplace (F21-F25) subies au moins par cette partie (18) de la lame fusible. L’invention concerne egalement un fusible, comprenant une enveloppe ceramique et au moins une lame fusible (16) disposee dans cette enveloppe, caracterise en ce qu’il comprend egalement des moyens de controle de l’environnement electromagnetique de la lame fusible (16) lors d’un regime pre-arc et/ou d’une transition pre-arc/arc par amplification ou attenuation des forces de Laplace subies par au moins une partie de la lame fusible (16).

In the above titled paper (ibid., vol. 25, no. 4, pp. 2464-2471, Oct. 10), six figures were printed incorrectly. The correct Figs. 2, 3, 4, 6, 7, and 10 are presented here.

A mathematical model and numerical experiments of pressure wave impacts with a porous medium are presented to simulate the valve burst out of a medium voltage switchgear and to evaluate the protection filter efficiency. A simplified one-dimensional gas flow model in porous medium with variable porosity is used. To solve numerically the governing equations, we employed the numerical method presented in Rochette et al. (2005) [18] to take into account the non-conservative term P(∂ϕ/∂x). Three sets of test are performed to study several filter prototypes. The objective is to provide a filter which does not produce a high reflected wave and cools enough the ejected hot gas. We first consider filters with variable porosity and simulate the interaction with an incident pressure wave, then we consider two types of granular material to characterize their incidence on the flow and finally, we simulate two different fluid flows (air and SF6) going through the porous medium.

Electrical power distribution equipment, such as medium-voltage (MV) switchgear, must be designed to withstand the pressures and temperatures of gases resulting from an internal arcing fault. An original way to limit the external effects of the arc consists in channeling downward the gas flow across a filter composed of a granular porous medium in order to absorb the abrupt pressure wave and to cool the hot gas flow. In this paper, we propose an optimization of the MV switchgear configuration to enhance the porous filter efficiency where we manage to strongly reduce the external manifestations of the arc fault. On one hand, we employ the numerical simulation tool lying on a physical model where the major events are taken into account. On the other hand, real experimental tests have been performed according to the IEC standards and pressure and temperature histories obtained by numerical simulation are compared with the experimental measurements.

This work deals with the comparison between calculations and measurements of pre-arcing times in High Breaking Capacity fuses under typical fault current conditions. This paper also describes the temperature evolution and the Joule energy dissipated in a fuse element during the pre-arcing time. By varying typical electrical parameters, namely the closing angle and the power factor, we show that various prospective currents such as those observed in industrial case can be fairly simulated. The pre-arcing time and then the clearing of the fault current are shown to be deeply dependent on these electrical characteristics. We exhibit simulated results of prospective current and supply voltage waves for given closing angles under two typical power factors which are compared with the experimental ones. A comparison between simulated pre-arcing times with experimental ones shows some discrepancies and a discussion on the numerical assumptions is made.

Pre-arcing stage is the first working step in high breaking capacity (HBC) fuse operation and affects the following step, namely, the arcing step. We have performed realistic HBC fuse tests for short (< 10 ms) and medium (> 10 ms) pre-arcing times by varying the phase angle of the electrical fault ( defined as the phase angle of the fault current once the supplied voltage is applied to the fuse) in the range from 0 degrees. to 160 degrees., for two values of the power factor (cos phi similar to 0.9 and cos phi similar to 0.1). Experimental values of the pre-arcing time and the arcing time (t(arc)) are given for t(prearc)/t(arc) less than or similar to 1 to similar to 4.2, and discussed from the energetic point of view by taking into account the inductive source term. The adiabatic assumption classically used in the modelling is also examined. The influence of the pre-arcing step on the arcing step is analysed by means of the Joule integral, the energy dissipated in the fuse and the mass and length of the fulgurite.

This work deals with the calculation of pre-arcing time in the case of High Breaking Capacity fuses submitted to high fault currents. The fuse elements studied consist of silver fuse strips with reduced sections in their centre. During the fuse working the fuse element is fused partly and hence vaporized. The time necessary to obtain an electric arc is called the pre-arcing time. This latter is defined by the duration from the appearance of the fault current to the splitting of the fuse element due to the vaporization of the reduced sections. The mathematic model is based on the solution of the heat transfer equation, using an enthalpy formulation to take into account the phase transitions, supplemented by an energy source due to the heat produced by ohmic losses. In order to determine the current density evolution in the fuse element, the Laplace equation governing the electric potential and the Ohm's law are used. Two typical fuse elements close to industrial ones are chosen for the simulations. The calculated pre-arcing times are given together with the main electrical properties, and compared with the experimental values. The resistive case with cos phi ~ 0.9 is discussed for a 2.5 mm and 7.5 mm-width elements respectively with one and three reduced sections.