Fluid-chemical modeling of the near-cathode sheath formation process in a high current broken in DC air circuit breaker

Abstract

When the contacts of medium-voltage DC air circuit breaker (DCCB) are separated, the energy distribution of arc is determined by the formation process of near electrode sheath. So, the voltage drop through the near electrode sheath is an important means to build-up the arc voltage, which determines the current-limiting performance of the DCCB directly. A numerical model describing the near electrode sheath formation process can provide insight into the physical mechanism of the arc formation and thus provide a method for arc energy regulation. In this work, a two-dimensional axisymmetric time-varying model of a medium-voltage DCCB arc when high-current interrupted was established based on a fluidchemical model involving 16 kinds of species and 47 collision reactions. The transient distributions of electron number density, positive and negative ion number density, net space charge density, axial electric field, axial potential between electrodes and near cathode sheath were obtained from the numerical model. The computational results show that the electron density in the arc column increases, then decreases, and then stabilizes during the near cathode sheath formation process, and the arc column diameter gradually becomes wider. The 11.14–12.33 V drops along the 17 µm space charge layer away from the cathode (65.5–72.5 kV/m) when the current is verying from 20–80 kA. The homogeneous external magnetic field has little effect on the distribution of particles in the near cathode sheath core, but the electron number density at the near cathode sheath periphery can increase with the magnetic field increasing and the homogeneous external magnetic field will lead to arc diffusion. The validity of the numerical model can be proved by comparison with the experiment.

Parametric characterization of arcs in semi-sealed splitter plate DC circuit breakers

“…Figure 13 illustrates the variation of electron density with the distance from the arc center after several repeated Fitting the median of the electron density to the distance from the center of the arc column in figure 13 reveals that the electron density distribution follows an exponential law of attenuation. The electron density is calculated as N e (r) = N 0 e −r/r0 (7) where r is the distance from the center of the arc column, N 0 represents the electron density at the center of the arc column, and it determines the overall level of the electron density distribution. r 0 is a length constant representing the length at which the electron density attenuates by 36.8%.…”

“…By studying arc motion characteristics and precisely measuring arc plasma parameters, assistance can be provided in determining the distance between splitter plates and their thickness. This is crucial for analyzing the breaking performance of DC circuit breakers and enhancing control techniques for such systems [7,8].…”