Effect of high-current pulsed arc on the evaporation characteristics of graphite electrode
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摘要: 气体开关电弧的热侵蚀作用是电极损耗的主要成因。石墨电极在电弧作用下发生蒸发并在多次放电后有明显的质量损耗，改变了开关内的气体环境和电极间距，导致开关动作可靠性降低。为研究石墨电极在脉冲电弧冲击下的侵蚀特征，基于开关电弧瞬态扩散特征和石墨材料参数，在弧根区域建立了电弧-电极能量耦合模型，得到了等离子体-固体区域的传热特性。考虑石墨电极的相变特征，计算瞬态热作用下石墨电极的加热范围以及临界相变点，研究瞬态电弧热冲击作用下的石墨电极相变机制。研究结果表明，电弧-电极界面热流主要集中在电弧接触面中心，电弧沉积的能量密度最高可达109 W/m2，石墨在电流上升初期基本处于加热状态，在能量积聚作用下，石墨转变为升华状态，传热强度随半径急剧衰减，蒸发区域略小于电弧半径。通过实验记录了5种开关工况下石墨电极烧蚀形貌和质量损失情况，结果表明，电极质量损失与电弧沉积在电极表面的能量线性相关，近似为0.015 mg/J。研究了电弧关键参数对电极质量损失速率的影响，为延缓电极损耗提供数据支撑。Abstract: The thermal erosion of arc is the main cause of electrode loss in the spark gap switch. The graphite electrode will evaporate and constantly undergo mass loss under the effect of the arc, which changes the gas environment in switch and the electrode distance, resulting in decreased reliability of the switch operation. To obtain erosion characteristics of graphite electrode under high-current pulse arc, the energy coupling model between the switching arc and graphite electrode is established based on the switching arc transient diffusion characteristics and graphite material parameters, and the heat transfer characteristics of plasma-solid region is obtained. Considering the phase change characteristics of graphite electrode, the heating range and critical phase change point of graphite electrode under transient thermal effect is calculated, and the phase change mechanism of graphite electrode under transient thermal shock of the arc is studied. The study results indicate that the heat flux of the arc-electrode interface is mainly concentrated in the center of the arc contact surface, and the energy density of arc deposition can reach up to 109 W/m2. Graphite is basically in a heating state at the beginning of the current rise, under the effect of energy accumulation, the graphite transforms into sublimation state. The heat transfer intensity decreases sharply with the radius decreasing, and the evaporation radius is slightly smaller than the arc radius. The ablation morphology and mass loss of graphite electrode under five different switching conditions were recorded through experiments. The experimental results show that the electrode mass loss is linearly related to the energy deposited on the electrode surface by the arc, approximately 0.015 mg/J. This paper studies the influence of arc key parameters on electrode mass-loss rate, and provides a theoretical and experimental basis for slowing electrode loss.
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Key words:
- pulse discharge /
- spark-gap switch /
- graphite electrode /
- switching arc /
- electrode erosion
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图 1 气体开关中石墨电极位置示意图
Figure 1. Schematic diagram of graphite electrode position in spark gap switch
图 3 5种典型的开关脉冲放电电流波形
Figure 3. Five typical switching pulse discharge current waveforms
图 8 石墨电极表面烧蚀宏观与微观照片
Figure 8. Macro and micro photos of graphite electrode surface ablation
图 9 不同放电时刻阳极表面石墨蒸气浓度
Figure 9. Mass fraction of graphite vapor on anode surface with time
图 11 阴极和阳极质量随放电次数的变化
Figure 11. Variation of cathode and anode mass with discharge times
表 1 计算模型边界条件的设置
Table 1. Setting of boundary conditions of MHD model
boundary type temperature/K electric potential magnetic potential AB, EF wall 1000 ${{\partial \varphi } \mathord{\left/ {\vphantom {{\partial \varphi } {\partial n}}} \right. } {\partial n}} = 0$ ${{\partial A} \mathord{\left/ {\vphantom {{\partial A} {\partial n}}} \right. } {\partial n}} = 0$ BC, DE, FG, HA wall 1000 ${{\partial \varphi } \mathord{\left/ {\vphantom {{\partial \varphi } {\partial n}}} \right. } {\partial n}} = 0$ ${{\partial A} \mathord{\left/ {\vphantom {{\partial A} {\partial n}}} \right. } {\partial n}} = 0$ CD wall (cathode) 1000 $j = - \sigma {{\partial \varphi } \mathord{\left/ {\vphantom {{\partial \varphi } {\partial n}}} \right. } {\partial n}}$ ${{\partial A} \mathord{\left/ {\vphantom {{\partial A} {\partial n}}} \right. } {\partial n}} = 0$ GH wall (anode) 1000 $\varphi = 0$ ${{\partial A} \mathord{\left/ {\vphantom {{\partial A} {\partial n}}} \right. } {\partial n}} = 0$ 
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