OPTIMIZATION OF TEST PROCEDURE TO IMPROVE INSULATOR PERFORMANCE UNDERHIGH ELECTRIC STRESS

Surface flashover properties such as the ultimate failure level, i.e., conditioned breakdown voltage, and insulation withstand strength i.e. , holdoff voltage of solid insulators, in relation to test procedures, are investigated for the first time. Four types of test procedures na mely, single cycle steady step, multiple cycle steady step, multiple s hot, and hill-valley test were adopted in the present work. The behavi or of the insulators under a given test procedure is explained on the basis of surface electronic defects and adsorbed gaseous atoms or mole cules. In general, the test procedures are found to influence signific antly the surface flashover properties of large band gap insulators su ch as polycrystalline alumina and single crystal quartz in vacuum. The steady step (both single and multiple cycle) tests are found to incre ase the degree of conditioning to a higher level (approximately 25% in crease in the case of alumina) during the second day test. However, th e samples subjected to these tests displayed a higher degree of decond itioning (approximately 40% decrease in the case of alumina), i.e., po or holdoff strength, during the second and third day test. A simultane ous increase of conditioning and decrease of deconditioning (i.e., hig her holdoff strength) is observed when the samples are subjected to ne w developed test procedures called multiple shot and hill-valley tests . The surface flashover performance of 6 mum finish alumina specimens (prepared under identical conditions), observed with different test pr ocedures, are also compared and discussed.