Analysis of the characteristics of DC nozzle arcs in air and guidance for the search of SF₆replacement gas

Abstract

It is shown that the arc model based on laminar flow cannot predict satisfactorily the voltage of an air arc burning in a supersonic nozzle. The Prandtl mixing length model (PML) and a modified k-epsilon turbulence model (MKE) are used to introduce turbulence enhanced momentum and energy transport. Arc voltages predicted by these two turbulence models are in good agreement with experiments at the stagnation pressure (P 0) of 10 bar. The predicted arc voltages by MKE for P 0 = 13 bar and 7 bar are in better agreement with experiments than those predicted by PML. MKE is therefore a preferred turbulence model for air nozzle arc. There are two peaks in ρC P of air at 4000 K and 7000 K due, respectively, to the dissociation of oxygen and that of nitrogen. These peaks produce corresponding peaks in turbulent thermal conductivity, which results in very broad radial temperature profile and a large arc radius. Thus, turbulence indirectly enhances axial enthalpy transport, which becomes the dominant energy transport process for the overall energy balance of the arc column at high currents. When the current reduces, turbulent thermal conduction gradually becomes dominant. The temperature dependence of ρC P has a decisive influence on the radial temperature profile of a turbulent arc, thus the thermal interruption capability of a gas. Comparison between ρC P for air and SF 6 shows that ρC P for SF 6 has peaks below 4000 K. This renders a distinctive arc core and a small arc radius for turbulent SF 6 , thus superior arc quenching capability. It is suggested, for the first time, that ρC P provides guidance for the search of a replacement switching gas for SF 6 .

Metal vapor content of an electric arc initiated by exploding wire in a model N2 circuit breaker: simulation and experiment

“…The arc temperature just near current zero (CZ) is less than 4 000 K. The thermal interruption capability of a gas is dependent on ρCp as a factor. the ρCp peak produces a corresponding peak in turbulent thermal conductivity, which results in a broad radial T-profile and a large arc radius [53]. For optimum thermal interruption performance, the ρCp should be as large as possible at temperatures below the 'T conducting ' (around 4000-5000 K) and as small as possible at higher temperatures [54].…”

Characteristics Analysis of Fluid Flow and Heating Rate of a Molten Bath Utilizing a Unified Model in a DC EAF

“…The thermodynamic and transport properties of the plasma arc (air) [18,[37][38][39][40][41], such as density, specific heat, dynamic viscosity, thermal conductivity, electric conductivity, and radiation coefficient [27], were taken from published literature, and are shown in Figure 2. The thermophysical properties of the molten steel used for simulation are listed in Table 2 [18,42].…”

The Performance of Insulation and Arc Interruption of the Environmentally Friendly Gas CF3I

“…In this paper, CF 3 I-CO 2 mixture, whose insulation strength is 97% of CF 3 I-N 2 in the same condition if the mixing ratio is 30%, is researched [3]. With this proportion relationship, insulation property of CF 3 I-CO 2 mixture relative to SF 6 and 20%SF 6 -80%N 2 can be calculated [4]. About the situation in highly nonuniform electric field, breakdown voltage of CF 3 I-N 2 mixture with the distances of 10 mm and 20 mm as examples is compared with SF 6 and 20%SF 6 -80%N 2 , as shown in Figure 2.…”