基于宏观—微观耦合模拟的电磁继电器触头动熔焊机理研究

Bounce occurs during the pickup process of relay contacts and may well lead to stick failure of a relay, which is a main failure model in switches. Recently, relationship between welding force and factors such as current and material were investigated mainly by experiments. However, research on the welding force calculation and welding mechanism from the view point of micro structure is rare, and most of them were based on evaluation of size and depth of welding area. Those model did not take the metallurgy phenomena in to consideration. This project will firstly model the bridge and welding pool characteristics to obtain the shape and dimensions of the liquid metal formated on the contact surface, and then will be focused on simulation the grain growth and micro structure of the welding area during the solidification process of the liquid metal through using the finite volume method and cellular automation method. Secondly, the micro structure will be used to calculate the physical properties of the welding area. Thirdly, a force calculation model will be created on the basis of the size and the physical properties of the welding area to evaluate the welding characteristics. Finally, experimental study on welding force and microstructure of welding area will be carried out to validate the model. This project will reveal the mechanism of stick failure model of the relay, and will provide the theoretical instrudtions for the reliability deisgn of the relay.

触头在闭合过程中回跳引起的动熔焊可以导致继电器发生粘连失效，是最主要的失效模式。目前多采用实验研究揭示闭合电流、材料因素等对熔焊力的影响规律，但从熔焊机理上揭示熔焊特性的研究相对较少，且多基于电弧对触头热作用估算熔焊区域深度和面积得到熔焊力。此类模型对于熔焊深度与面积的估算过于简化，且没有考虑液态金属区域冶金过程的影响。本项目从闭合过程中的液桥回跳和电弧回跳出发，建立描述液桥和熔池内部温度、流场、相变以及形变的耦合模型，获得液态金属区域几何尺寸。采用宏观有限体积法-微观元胞自动机耦合法模拟液态金属凝固后的微观组织结构，得到熔焊区域的物性参数。根据熔焊区域几何尺寸和物性参数建立熔焊力计算模型，较为准确地评估熔焊力的大小。最终，研制熔焊实验系统，通过测试熔焊力和微观组织结构验证模型的正确性。本项目将从根本上揭示电器触头粘连失效的机理，具有重要的科学意义，并可为继电器可靠性设计提供理论依据。

主要针对电磁继电器产品的动熔焊失效机理进行研究。首先，利用Fluent建立触头熔池模型，得到回跳电弧作用下触头表面熔化区域体积。在此基础上，利用有限元分析软件Marc建立熔焊力预计模型，计算得到了回跳电弧导致的熔焊力。最后，设计了高压直流大功率继电器熔焊实验系统，研究了不同触头开距、磁吹强度及分断速度单独作用以及耦合作用下熔焊规律。主要研究成果如下：(1) 建立了回跳电弧作用下触头熔池特性的仿真模型，得到回跳燃弧导致触头熔化区域的半径和体积。(2) 利用有限元软件Marc建立了触头分断时熔焊区域等效模型。当熔焊区域直径不变而高度越小时，熔焊力越大；当熔焊区域高度不变而直径越大时，熔焊力越大。熔焊区域体积不变而直径高度比改变时，“矮胖型”熔焊区域比“高瘦型”熔焊区域更难拉断，即直径高度比越大，熔焊力越大。熔焊区域体积不变而屈服强度变大时熔焊力也增大。(3) 设计了以PCB208C01系列压电式力传感器为核心的熔焊力采集模块以及以基恩士LKH-055高精度激光位移传感器为核心的回跳信号采集模块。采用了在阴极静触头和阳极静触头安装两个力传感器的结构较好地解决阴极静触头和阳极静触头熔焊力出现时刻的不同步性问题。提出了熔焊力幅值提取方法，实测表明，采用“触头完全分离后力传感器输出信号与熔焊发生时力传感器输出信号最大值之差”和“熔焊区域断裂点与熔焊力最大值点之差”来表征熔焊力较为准确。(4) 单因素实验表明：减小触头开距有利于减少熔焊的发生，增大磁吹强度有利于减少熔焊的发生，,提高分断速度有利于减少熔焊的发生.正交实验表明，熔焊力影响显著度依次为分断速度、磁吹强度和触头开距。