Antoni Klajn

Switching vacuum arc in a pulsed transverse magnetic field

An experimental analysis of the vacuum arc behavior in a pulsed transverse magnetic field with amplitudes up to 120 mT and frequency of 900 Hz is presented in the paper. The arc was produced between Cu contacts during the switching-off operation of the current half-wave of amplitude 500 A and frequency of 30 Hz, so that the circuit parameters had rather moderate values which are easy to obtain in a vacuum switch. The presented results are a part of work which aims to examine the possibilities of using transverse magnetic fields to force a current interruption in vacuum. The analysis was performed using high-speed photography (2000 frames/s) and a shielded Langmuir probe. The results obtained show that the plasma movement and the displacement of the arc in the oscillatory magnetic field proceed according to the Lorentz force acting on ions. This arc displacement is in accordance with the retrograde motion known from the literature, which is opposite to that resulting from the Amperian force. Arc voltage increases of up to about 80 V were observed during the magnetic field action, but the current flow remained undisturbed.

Langmuir probes in switching vacuum arc measurements

Some properties of the Langmuir probes used in measurements of electron parameters in a vacuum switching arc are reported in the paper. Two shapes of the probe: plane and Faraday-cup one, placed at various distances from the arc column, were compared. Also some shields of probes were tested. Probes were supplied with a saw-tooth potential as well as with a constant one. The arc current was a sine half-wave with amplitudes from 400 A up to 1400 A, generated in an oscillatory low-voltage circuit. The electron parameters: temperature, thermal velocity and density were measured. The comparison of statistical distribution of results and its accuracy illustrate the relation between various probe shapes, shielding and the probe distance from the arcing contacts. The best accuracy of measurement was observed in case of the respective probe shielding or the proper distance between the probe and the tested vacuum arc. Finally some additional criteria, which can be useful in choosing of the Langmuir probe in measurements of the low voltage vacuum arc plasma parameters were proposed.

Experimental analysis of ion parameters during the forced vacuum arc interruption

The paper presents experimental measuring results of the ion decay time during the post-arc phase after a forced interruption of diffuse vacuum arc. Arc current of amplitudes 400 A and 600 A was switched-off using counter-pulse current with falling rates from 2 A//spl mu/s u to 67 A//spl mu/s in a laboratory test circuit. The used voltage, current and contact parameters were representative for a low-voltage vacuum switch. The decay process of ion current was observed, using a retarding field analyser. First, a series of introductory measurements concerning probe calibration were performed. The decay times of ions were measured as function of the falling rate of the counter-current, and mean values from about 60 /spl mu/s at arc current falling rate 2 A//spl mu/s up to 35 /spl mu/s at arc current falling rate 67 A//spl mu/s were measured. Only a small dependence of the decay time from the arc current value (400 A or 600 A) was observed. The decay time decreases significantly with increasing of the counter-current failing rate. The results are proposed as a parameter in the modelling of post-arc phenomena of low voltage vacuum switches.

Analysis of a forced extinction of a diffuse vacuum arc for digital modelling purposes

The decay time of electron current in the post-arc phase after a forced interruption of a diffuse vacuum arc were measured experimentally. Arc current of amplitude 400 A was switched-off using counter-pulse currents with failing rates from 3 A//spl mu/s u to 30 A//spl mu/s. The decay process of electron current was observed using a Langmuir probe. The decay times of electrons of mean values from 4.5 /spl mu/s up to 6 /spl mu/s were measured Considering the flying times from the contact edge to the probe at current zero, the decay times of electrons can be estimated in the, range from 0, 5 us up to 3 /spl mu/s. These values are proposed as electron deceleration time in modelling of post-arc phenomena for low voltage vacuum switches.

Characteristics of flicker depending on network loads

Peculiarities of different kinds of load in relation to produced flicker effects are presented in the paper. The analysis bases on the measurements performed in low voltage installations of an industrial object using a conventional power quality instrument. Selected types of the load: laser-cutting machines, welding devices and electrical drives were chosen in order to observe the specific properties of flicker produced in these circuits. Some differences of short-time flicker severity in relation to load type were exposed and discussed. Unfortunately, during measurements it was not possible to separate the influences of other load in the analysed network, so the observed voltage was disturbed by the selected load as well as partially by other devices supplied from the same network. However, the specific peculiarities of analysed load were observed and discussed. Furthermore, the measured values of the short-term flicker severity, registered according to the standard EN-61000-4-15 was compared with the ratio of the voltage changes in the network. Based on these observations some critical evaluation of obtained measuring results in relation to the physical sense of flicker effects were discussed. The analysed load was characterised by current flow as well as the number of changes in a given time interval. The obtained results, after a more detailed analysis could be used in the future for identification of the disturbance sources in the network.

Ion Parameters After Forced Extinguishing of the Diffuse Vacuum Arc

Results of ion parameters measurement during the counterpulse arc interruption in a vacuum are presented in this paper. The experiments were performed in a laboratory arrangement with a demountable vacuum chamber equipped with a Cu-contact system representative for the low-voltage vacuum switches. The applied vacuum arc current with values of 400 and 600 A was interrupted at falling rates from 2 up to 90 A/mus. The following ion parameters were examined: the decay time of ions after the current zero, ion energy, and residual charge. The mean values of the ion decay time varied from about 35 mus at a falling rate of 2 A/mus to about 20 mus at 90 A/mus and diminished with the increasing falling rate of the arc current. The ion energy grew with the growing of the forced falling rate of the vacuum arc current, and its mean values varied from 54 to 99 eV. The residual charge diminished with the increasing of the arc current falling rate, and its values varied from about 9 to about 31 muC in the tested conditions. The presented results can be useful in modeling and design.

Plasma parameters after a forced extinguishing of the diffuse vacuum arc

A series of experiments were performed in order to optimise the forced vacuum arc current commutation with the counter-pulse current method. The experiments were performed in a laboratory arrangement with parameters representatives for the low-voltage vacuum switches. The tested vacuum arc current with values 400 A and 600 A was interrupted with a counter-pulse current at falling rates from 2 A/mus up to 90 A/mus. The main measured parameters were: ion energy and residual charge after the current zero as function of the forced falling rate of the arc current. The results can be useful in modelling and design.

Experimental analysis of diffuse vacuum arc in a transverse magnetic field

Measuring results of vacuum arc voltage under the influence of a transverse magnetic field are presented in the paper. The arc current half-wave had amplitudes from 100 to 600 A and frequency of about 30 Hz. The field was oscillatory (450 and 900 Hz, amplitudes from 15 to 200 mT) as well as proportional to the current values. Arc voltage in relation to field density, arc current and contact distance were observed and discussed. Arc photographs (2000 frames/s) show constriction of the arc and its motion according to Lorentz force acting on ions.

Evaluation of residual charge after a forced extinguishing of the vacuum arc

The paper presents results of an experimental and theoretical analysis concerning the observation of the post-arc phenomena in plasma after the forced extinguishing of a diffuse arc in vacuum. Examination applied, among other things, evaluation of the residual charge. Experiments were performed in laboratory conditions using a de-mountable vacuum chamber equipped with Cu flat contact system. The switched-off arc current had the form of a half-wave with amplitudes of 400 A and 600 A and frequency of 30 Hz. The source of this current was a capacitor bank, loaded before each switching process. The voltage of loaded capacitor was in range of few hundreds Volts, so the examined arc was low voltage and diffuse one. The forced extinguishing had been realised by the counter-pulse current with falling rate in range 2÷90 A/μs. The measurements of post-arc plasma was performed using retarding field analyser (RFA), witch worked in electron separation mode, measuring ion current. The ion current after extinguishing of the arc was the basis to evaluation of the residual charge. The peak post-arc current was the range (2-7) A and residual charge (10-30) μC in the tested conditions. The results could be used in modelling of post-arc phenomena in vacuum.

Experimental analysis of a vacuum arc connected parallel to an arc in air

The vacuum arc is distinguished with many parameters from the arc in air. In some technical applications there occurs the question about phenomena which could be observed when an air arc will be connected in parallel with an arc in vacuum. The aim of the work is to present some experimental observations and discuss this problem. The experiments were performed in a laboratory circuit, in which an electrical arc burning in air was connected in parallel with a vacuum arc. The arc current had the oscillatory AC form with amplitudes of about 600 A, at supply voltages up to 1200 V. The vacuum arc was initiated in a special vacuum chamber, equiped with an ignition electrode, using high voltage triggering shortly after air arc initiation. The parameters of both discharges were observed, particularly the voltage and current flows after the time instant of the parallel commutation. The main question was the existence possibility of both these kinds of electrical discharge in the same electrical circuit. Experiments showed that in suitable circuit parameters, the arc in air is successfully extinguished by the vacuum arc. The discussion of observed phenomena are presented in the paper.