Visualization and multi-signal measurement of electrodynamic lift and associated contact welding in electromechanical relays under instantaneous overload

This paper investigates the electrodynamic lift and contact welding in electromechanical relays subjected to overload currents on the 1–8 kA with durations of 0.6 ms. The study employs light-shadow visualization and image processing to characterize the contact traces, combined with the multi-signal measurement of the instantaneous electromechanical coupled response. A critical boundary for the occurrence of electrodynamic lift, determined by initial contact force and peak overload current, has been identified. Electrodynamic lift induces arcing and the molten pool formed after arc extinction during contact rebound solidifies and causes welding upon closure. Meanwhile, a sufficiently large lift distance prolongs the cooling time of the molten pool, thereby suppressing welding formation. The results may provide a reference for the design of spring contact components under overload current conditions to minimize contact welding strength.