Experimental Study on Electron Density Change of Low Voltage AC Arc Under Different Currents

In recent years, magnetic fluid and arc plasma simulation models based on local thermodynamic equilibrium have provided an important aid to the analysis of the arc characteristics of switching appliances. However, it has been shown that when the current is small, the arc as a whole is deviated from the local thermodynamic equilibrium, but a clear correspondence between the arc current and the thermodynamic state of the arc is not given, which largely reduces the reliability of the simulation model. In this paper, from the perspective of arc spectral analysis, we build an arc experimental platform with spectral measurement function. Through this platform, the atomic spectral line data of the carbon electrode in the arc gap at different currents are measured, and the electron density data are obtained by the Boltzmann plot method and the Stark broadening method. The measured results show that when the current is greater than 40A, the electron density of the arc-firing process reaches above l022/<inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">cm</inf>3, which is consistent with the recognized data (>1022/<inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">cm</inf>3) under the local thermal equilibrium. When the current is less than 40A under the same condition, with the increase of current, the arc electron density increases and tends to l022/cm<sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sup>• The change of arc electron density indicates that the arc thermodynamic state is more inclined to the nonlocal thermodynamic equilibrium when the arc current is less than 40A. From this, we can get the inference that the thermodynamic state of low-voltage AC arc and the size of arc current have a corresponding relationship, when the current is greater than 40A, the arc as a whole is more inclined to the local thermodynamic equilibrium state, and vice versa is more inclined to the non-equilibrium state.