Electrical Properties of Ag-C Contact Materials Containing Different Allotropes of Carbon
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Arc erosion of high current contacts in the aspect of CAD of switching devices
The author addresses the problem of using available experimental data to study the erosion behavior of high-current contacts and various contact materials for computer-aided design (CAD) of low-voltage switching devices. Computer modeling of switching phenomena in these devices is described. The contact erosion is discussed for contacts operating in air at atmospheric pressure, for the current range 10-1000 A and 1-20 kA. A computer-controlled system for testing contacts in the automatic sequence for both current ranges is discussed. Accelerated testing and statistical evaluation of the contact material in simulated AC and DC conditions at constant arcing is possible. Results of the study of quantitative and qualitative relations between the material loss of contacts and the number of switching operations, and the arc current-time integral and the arc energy for various composite materials used in the power switching devices are given. The influence of contact dimensions on the dynamic arc voltage characteristic and the arc energy and the material loss at high currents is discussed. Empirical equations for the arc voltage and the contact erosion are given.<<ETX>>
The Effect of Unsymmetrical Material Combination on the Contact and Switching Behavior
Contact materials for electrical power engineering in symmetrical and unsymmetrical combination are investigated with respect to welding resistivity, contact resistance, arc motion, and arc erosion, under special consideration of Ag/C. In combination with Ag/C, the welding resistivity as well as the contact resistance of W/Ag and copper are improved. The arc staying time shows a distinct polarity-dependence in the region investigated (l = 350-1800 A). The erosion is also dependent on the polarity. It coincides with the values that can be calculated from the anode and cathode erosions of the symmetrical combinations.