Gérard Velleaud

A study of the influence of the walls' nature on the behaviour of a low-voltage arc breaker by means of an inverse method

The evolution of an inverse diagnostic method used to study a low-voltage arc breaker is presented. The treatment of induction measurements obtained outside the arc breaking set-up allows us to reconstitute the arc dynamic. The arc is simulated as a multi-linear thread-like line sliding between two parallel rails. We used this method in order to study the behaviour of the arc for arc-breaking chambers composed of several materials and for various intensities of the current. We also calculated the values of , where is the arc conductivity and S is its cross section and, in some cases, we evaluated the values of the arc cross section.

Evolution of a low-voltage electric arc

The evolution of a low-voltage electric arc is studied with a matrix of microcoils which behaves like a magnetic camera. The arc is assimilated to a series of straight segments. The shape that it assumes in the electrode gap as well as re-striking phenomena are analysed. The influence of insulating and conducting obstacles is stressed.

Experimental study of HBC fuses working at short and medium pre-arcing times

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) 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° to 160°, for two values of the power factor (cos φ ∼ 0.9 and cos φ ∼ 0.1). Experimental values of the pre-arcing time and the arcing time (t are ) are given for t prearc /t MC ? 1 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.

Study of the low-voltage electric breaking arc restrike by means of an inverse method

This paper presents a method to study the dynamics of an arc from magnetic measurements. The mathematical model developed enables us to reconstitute the evolution of a low-voltage, self-blown arc assimilated to a succession of current elements. It also enables us to analyze restrike phenomena for which one might suppose there exists a current exchange between an arc located at the top of the electrodes and another one located in a zone where there remains some possibility of conduction.

A study of the kinematics of a low-voltage breaking self-blown arc: analysis of the derivative of the anode-cathode voltage

The comparison between the derivative of the arc voltage function and the travel of a self-blown arc column shows that the distribution of the function peaks is in agreement with the displacement of the anodic roots. This enables the authors to describe the characteristics of the moving column arc with a good accuracy.

Use of an inverse method on the determination of the evolution of a self-blown electric arc in the air

An inverse method for studying the dynamic behavior of a low-voltage arc column is presented. A small number of microcoils are placed at suitably chosen points. The measured inductions are recorded during the whole arc life, and the evolution curves of the position of the anodic and cathodic roots, as well as those of the arc column gradient, assumed to be threadlike, can be obtained analytically. From such results it is easy to define the speed and acceleration of the anodic and cathodic roots, allowing the column behavior to be defined during the entire blowing phase. Moreover, the geometry of the breaking device is the only factor that must be taken into account. >

Study of the movement of an electric breaking arc at a low voltage

The experimental study of the evolution of the electric arc, with inverse movements is made possible with good accuracy thanks to the use of microcoils which detect the induction created by the electric circuit. The simulation of the movement of the arc and of the magnetic induction against time allow the authors to explain satisfactorily the measurements made during the rising phase.

Measurement of the pre-arcing time and the fulgurite length in hbc fuse in the case of tests performed with an A.C. 100 KVA station

This study deals with a specific test device especially designed to perform tests on HBC fuse on a scale of a non industrial laboratory. In fact it is not possible for most of academic laboratories to build up a device supplying the same current and voltage ranges as in an industrial test station. Moreover the capacitor bank discharges are often used in academic laboratories to test electric fuses. But the main drawback of the capacitor bank is to supply a non 50 Hz-sinusoidal current waveform for one half period only. We present the first measurements performed on experimental HBC fuses using a 100 kVA station built up from a single phase transformer. These first measurements are performed using various fuse elements with the same geometries as in industrial fuses of the middle voltage range. The filling material is silica sand or quartz sand and it is chosen with the same properties as in industrial fuses. The fuse working is studied experimentally on the whole duration of the fuse working which depends on the values chosen for the power factor and the closing angle. The results are given for the pre-arcing time and the fulgurite length. The power factor put in the tests is equal to cos phi~ 0.9 and cos phi ~0.1, and the closing angle is increased from 0 deg to 180 deg. The results are discussed by taking into account the influence of the energy to dissipate, namely the Joule energy and the inductive energy.

Study of the SIO 2 plasma radiation. application to the fuse arc plasma

During the HBC fuse working, the fault current implies the initiation of an electric arc which is composed of metallic species vapours mainly, generally silver. This defines the end of the pre-arcing time. This electric arc interacts quickly with the surrounding silica sand grains or quartz sand. Thus a silver plasma is formed around the reduced sections of the fuse element. This silver plasma interacts with the silica sand grains and this interaction gives rise to the ignition of a plasma composed of vapours resulting from the dissociation of the SiO2 molecules. The radiation escaped from the SiO2 plasma can be used to assess experimentally the temperature (T) and the electron density (ne), two fundamental parameters for modelling purposes. T and ne are difficult to interpret because of the strong gradients in pressure, temperature, and material densities from the centre to the surroundings where the measurement is done. We propose a first formulation to calculate this radiation in order to increase the understanding of the radiation measurements.