Abstract
This paper presents results of a theoretical and experimental investigation of the phenomena of electrical contact repulsion and its associated blow-off characteristics at high current. The voltage and current waveforms as well as contact's displacement oscillograms are recorded for analysis. The mathematical model of the phenomena based on differential equations for the arc, forces, contact heating and evaporation and displacement of the movable contact piece is elaborated to describe repulsion dynamics. All stages of contact separation including opening start, Joule explosion of the constriction zone and arcing are considered in series. It is found that side by side with electromagnetic force, which is responsible for the initiation of contact opening, thermal force due to vapour pressure, which develops further contact separation, is also very important and should be taken into consideration. Dependence of thermal force on voltage, current, circuit parameters and properties of contact material are calculated theoretically and examined against data obtained experimentally for the asymmetric contact pair AgC-AgNi.
Highlights
D YNAMICS of contact blow-open forces are very important to provide the desired opening conditions during a short circuit current for a reduction in arc duration and welding probability. It is suggested [1] as a rule that two forces appearing in closed contacts at the inrush of short circuit current are mainly responsible for characteristics of contact separation at the blow-off process
When magnetic force becomes equal to contact spring force, contact separation starts, which accompanied by an increase of current density and temperature up to melting point and the liquid bridge formation
It should be noted that presented above mathematical model may be simplified significantly if we use the experimental information about contact displacement for direct calculation of acceleration and total force rather than for verification of the model
Summary
D YNAMICS of contact blow-open forces are very important to provide the desired opening conditions during a short circuit current for a reduction in arc duration and welding probability. The method described for this aim in the paper [6] is based on the dependence of arc electrical conductivity on the arc temperature, which is different for different pressures, but it enables one to estimate average values of blow-open force using their experimental data and Yos’s theory for arc conductivity-temperature relationship [7]. Some noticeable discrepancy between results of calculation and experimental data due to simplification of this model indicate that a more detailed time-dependent description of all phenomena at the blow-open process which includes the arc and contact temperature, phase transformation, forces interaction have to be considered
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