Analysis of Contact Welding Mechanisms for On-Board Electromechanical Relays Withstanding kA-Level Inrush Current

Low-current switching devices are prone to contact welding failure when subjected to kA-level inrush currents. This article experimentally investigates the contact welding behavior and its underlying mechanisms of the on-board electromechanical relays that can withstand a maximum inrush current peak of 8 kA. The research methodology commences with a custom-designed test rig that is capable of in situ measurement of electrical and mechanical signals, as well as real-time synchronous observation of contact motion states. Three distinct contact welding regimes, namely, static contact welding, intermittent arc welding, and sustained arc welding, were explicitly identified, characterized, and interpreted. The corresponding occurrence conditions of inrush current, peak value, and duration are also presented in detail. Furthermore, the microscopic surface morphology characteristics resulted by three contact welding regimes were analyzed comparatively. Finally, a quantitative analysis was performed on the effects of inrush current peak value, duration, and static contact force on the heat generation responsible for contact welding. The underlying mechanisms accounting for the disparities in the resultant welding forces are elucidated. Distinct from existing theoretical models, this study establishes a comprehensive contact welding map covering peak inrush currents of 1 ∼ 8 kA and inrush current durations of 0.4 ∼ 0.8 ms, providing a predictive design guideline for determining the critical contact breaking force required to prevent welding failure under specific inrush current conditions.