电触点动熔焊奇异现象：分离熔焊及其燃弧特性研究

Dynamic welding is one of the most important topics in the area of electrical contacts. Experiments in recent years indicate some strange behaviors in contact welding, which is quite different from the traditional popular results or conclusions, i.e. the dynamic welding may occur in contact separation rather than in close operation ; short bounce arcing can results in stronger welding strength than longer bounce arcing. The above strange behaviors have been neither explained reasonably and clearly nor understood by the community of electrical contacts. Therefore two basic problems in dynamic welding of contact are not clear until now and need further research with different experiment conditions, i.e. (1) where is the exact position of dynamic welding occurrence? is it in separating or in closing movement and which is dominant? (2) What is the actual relationship between the dynamic welding and the arcing duration as well as the arcing length? is there a corresponding threshold value? The objectives of this proposal is to try to find the solution of the above strange problems or behaviors. The contact operation simulation system is used in this research to observe the real position of welding occurrence and its arcing behaviors with the modification of contact force, displacement, gap, velocity of closing and opening, contact materials, ambient atmosphere, current and voltage etc. Theoretical analysis will be conducted with the time sequence method, i.e. beginning from the stable connection Joule heating, to molten pool, separation molten bridge, metallic phase arc, material transfer, re-bridge, re-constriction, until the final molten bridge solidification for the case of welding in separation. And the investigation will be finished for the growth competition among the velocities of separation, material transfer bridging and molten bridge solidification. This research is much helpful for better understanding basic knowledge of contact welding and development of advanced power switching technology and its devices.

动熔焊是电接触研究中的最重要主题之一，近年来国内外针对触点动熔焊的实验研究发现了有悖于传统主流结论的奇异现象，即动熔焊发生于触点分离过程而非闭合过程，强熔焊主来自短弹跳电弧而非长弹跳电弧。此奇异现象至今尚无系统合理的机理解释，也缺乏系统深入的多条件实验测试分析。因此，关于动熔焊的两个基本问题尚无清晰肯定的结论，即（1）动熔焊到底发生在什么阶段？是分离过程，还是闭合过程，二者谁更主要？（2）动熔焊的发生与当时燃弧时间、电弧长度到底是何关系，有无临界值？本项目即针对此展开实验与理论研究，利用触点模拟实验系统研究触点压力、位移、开距、合分速度、触点材料、工作气氛、电流、电压等机电参数改变时，触点熔焊发生的位置及其燃弧特性规律。开展基于时序特征的分离熔焊理论研究，探讨分离运动速度、转移桥接速度、液桥降温凝固速度三者竞争关系。为抗熔焊新型开关电器的研发提供基础理论和技术依据。

随着可再生能源分布式电源、直流配电系统的快速发展，直流高压继电器接触器等高指标控制电器研发成了迫切需求，其中小型化、长寿命、大容量是此类开关电器的技术难点，而造成此难点的核心技术问题是触头易熔焊。如美国GIGAVAC公司高端G系列直流继电器/接触器在体积仅约128mm xΦ61mm情况下，可在25kVdc/30A-110A大容量下实现通断操作，但其抗熔焊能力较差，无法满足系统及用户要求，我国目前更无法独立自主制造出如此高指标开关电器。其关键原因之一是对制约开关电寿命的触点动熔焊故障机理了解不深不细。.本课题通过开展14-500Vdc/10-200A多种电流电压、CuCr/CuW/CuMo/AgSnO2/AgNi等多种触头材料、氮气/氩气/氧气等多种环境气氛及多种分断力等复杂条件下的实验与理论研究，首次提出触头分离熔焊机理是因为电极材料喷溅转移形成的触头间多液桥散热不平衡所致。即触点分离时液桥爆炸形成金相电弧（对应电弧电压约10V、几十微秒电压脉冲），金相电弧造成强烈触点表面多点液滴喷溅及极间材料转移，进而在动静触点间隙形成多个液桥，导致间隙电路短接而使触点电压回归为零。由于多个液桥在体积、电阻、位置、散热、分流值等方面存在差异和不平衡，其中某一个液桥率先冷却凝固导致触点表面局部熔焊，由于单点小面积熔焊即具有较高熔焊强度，进而造成整个触点出现无法打开的永久熔焊现象。.澄清了分离熔焊前电压窄脉冲不是机械弹跳和接触电阻所致，而是金相电弧与喷溅液桥。研究了气氛物性参数与触头分断燃弧时间之间定量解析数学模型，阐明了比热、原子量、传热系数、电子亲和性等物性参数对燃弧影响规律，对于深入了解分离熔焊物理实质及气氛性质对燃弧时间影响机理，研发高抗焊触头材料及设计抗熔焊、低燃弧气氛具有重要学术与工程实际意义。代表性成果发表在IEEE TCPMT 2016.NO.6并上封面重点推介。