Insulator surface conduction state and surface flashover voltage

The withstand of aged and or contaminated insulators has to be tested in a humid environment under controlled conditions. However, during the humidification the conduction state of the aged and/or contaminated insulators shows a temporal variation. The time at which the maximum conductance is reached depends on the insulator material, design, humidification rate and the severity of contamination. The results of this work show that the maximum conductance of naturally aged and/or contaminated composite polymeric insulators under moderate humidification conditions is reached after a time in the order of one hour. However, contaminated ceramic barrel insulators conductance is reached after a much longer time which is of the order of a couple of hours. The presented results show that when the test voltage is applied at the time when the conductance of the insulator is maximum the electric withstand of the insulator is in its minimum.