Optimization of test procedure to improve insulator performance under high electric stress

Surface flashover properties in relation to test procedures were investigated, using single-cycle steady step, multiple-cycle steady-step, multiple-shot, and hill-valley tests. In general, the test procedures were found to influence significantly the surface flashover properties of large-bandgap insulators such as polycrystalline alumina and signal-crystal quartz in vacuum. The steady-step tests increased the degree of conditioning to a higher level during the second day. However, the samples subjected to these tests displayed a higher degree of deconditioning during the second and third day. A simultaneous increase of conditioning and decrease of deconditioning was observed for the multiple-shot and hill-valley tests. The surface flashover performances of 6- mu m-finish alumina specimens for different test procedures are also compared and discussed. The behavior of the insulators under a given test procedure is explained on the basis of surface electronic defects and adsorbed gaseous atoms or molecules. >