| A review of the experimental and theoretical work performed on understanding electrode erosion in high current transient arcs is given. Over 250 references from the last 40 years are cited, including many recent translations of Russian and German literature. The major mechanisms leading to electrode material melting, vaporization, and removal are identified and discussed as a function of physical and design variables, as well as their effect on electrode erosion rates. A solution to the one-dimensional heat conduction equation, ignoring the effect of electrode joule heating, is discussed and is found to be adequate to explain many experimental results as well as provide a systematic method for classifying different methods used to reduce electrode erosion. Several models which include joule heating due to the skin effect are also evaluated and in both cases rankings of electrode material performance are given. State of the art curves are given for electrode lifetime as a function of charge transfer (0.1 mC to 1 kC per shot) and peak current (1 kA to 1 MA) form the data of 25 different authors.; The author's own experimental results are given for electrode erosion in high current (up to 500 kA), high energy (up to 35 kJ per pulse) transient arcs. Electrode erosion rates were measured for an oscillatory current pulse (100-250 kHz) as a function of electrode material (over 20 different materials), charge transfer (0.5 to 30 C per shot), peak current (50 to 500 kA), electrode diameter (1.27 to 2.54 cm), gap spacing (0.15 to 2.0 cm), gas type (Air, Ar, He, N{dollar}sb2{dollar}, SF{dollar}sb6{dollar}) and gas pressure (0.87 to 3 {dollar}times{dollar} 10{dollar}sp5{dollar} Pa). Scaling laws were derived from the thermal model which agree well with experimental results from several sources. A simple model is also used to predict the minimum in the erosion rate for electrodes composed of two materials. |
