High Current AC Break Arc Contact Erosion

Contact break arc erosion fundamentals applicable to high power switching devices in air (e.g. air- magnetic circuit breakers and contactors) are reviewed along with recent results showing dominant factors that affect contact erosion in the range of 3 kA_p to 22 kA_p. Background covers a review of arc plasma theory pertaining to contact erosion in air at atmospheric pressure including metallic bridge formation, metallic-to-gaseous arc phase transition, plasma sheath formation, anode and cathode erosion, contact area effects, material composition, manufacturing methods, and metal vapor jet formation. One of the significant results from this data was that current density increased and erosion dramatically increased as the arc root area approached the contact surface area dimensions. Transient values for power density, current density, and arc conductivity were also measured using synchronized waveform acquisition with high-speed video to provide useful data in a current range where there is little published data available. High-current molten metal bridge results are also presented from the corresponding erosion test data that illustrate the many different types of bridge formation and voltage waveshapes at contact part. The theory and the experimental data presented will be useful for those who model contact erosion or need to understand the critical factors and the degree to which these factors can affect contact erosion.