Contact current carrying limits

Transient contacts, such as those in railgun armatures, operate near the limits of metal-metal contacts. When the current-carrying limit of a contact is exceeded, the contact makes a transition from a low-voltage state (typically less than 1 V) to an arc with high-voltage (typically 30 V or greater) and leads to high erosion of the slider and substrate. Experiments were performed on metal contacts at current densities typical of railgun armatures (>1 GA/m²). It was found that the classical theory of electrical contacts did not support observations. A theoretical description to support the experimental observations was developed. The theoretical concept is based on the assumption that, under the experimental conditions considered, the contact is adiabatic. Transition of the contact then depends on resistive heating of the contact area. A computer simulation predicts when the contact will make the transition to arcing. It is suggested that a contact should be made with a material with a high action to vaporize, such as copper. Since the contact is adiabatic, only the contactor surface zone is critical