Current concentrations in high voltage pulsed electrical contacts
Senft, Brian Zephraim Cowell
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The motivation for the research is to investigate current concentrations leading to material damage for flat-on-flat metal electrical contacts under pulsed high currents and plastically-loaded operating conditions. To provide a model capable of predicting the performance of a high current electrical pulse material, the material’s ability to distribute current densities evenly within the electrical contact interface, and the material’s ability to transmit high current density loads without vaporizing was ascertained. Experimental validation of the models was then performed to assess the accuracy of the electrical contact material performance predictions. The key material properties of interest in the research are electrical resistivity, magnetic permeability, melting temperature, boiling temperature, specific heat capacity, and enthalpy of fusion. Electrical parameters included the rate of release of current from the capacitor banks, peak magnitude of current, and duration of current pulse. First, electrical current pulses of varying magnitudes were delivered to test specimens of identical composition and dimensions fixed between two copper rails with a flat-on-flat contact interaction. Next, at a fixed current pulse level, specimen material composition was varied to observe the effects of material parameters on electrical contact characteristics. Testing materials included aluminum, zinc, and steel. Additionally, effects of geometrical factors were studied by testing the design of an aluminum armature often used in an electromagnetic launcher. Finally, sliding electrical contact tests were conducted using the armature to analyze variations in the electrical interface characteristics as compared to the static tests. The experiments resulted in the development of molten electrical interfaces, signs of localized hot spots, and wear of electrical contact interfaces as shown by surface profilometry. The research presented extends previous work, which has primarily focused on the performance electrical contacts operating at steady state and predominately at lower current levels. The study has achieved a unique method of characterizing performance of electrical contact materials under high current electrical pulse conditions by solving a material’s current density load limitations, a material’s effectiveness at current distribution (based of material properties, mechanical loading, and electrical loading) and by providing insight into the complexities of experimental testing of electrical contact materials under high current electrical pulses. The result is the capability of predicting failure of electrical contacts under high current electrical pulse due to current concentration at the electrical interface.