Insulating properties of some liquids after an electrical arc

The insulating properties of a liquid are commonly studied before a breakdown occurs. In HV industrial apparatus such as high energy plastic metallized and liquid impregnated films capacitors, some local breakdowns, named self-healing, occur and the ability of the liquid to remain insulating after electrical degradation is of interest. To understand the influence of the liquid on the behavior of such capacitors, the post-arc behavior of the liquid alone has to be studied in a range of energy (~mJ) close to the self-healing process. The present work deals with the study of the ability of different liquids to restore in the millisecond range their insulating property after an electrical arc. Using an experimental apparatus based on the repetitive charging with a dc HV generator and discharging through an arc of a resistor-capacity system, different kind of liquids were tested. The liquids we used were alcane, esters, alkyl benzene and polyaromatic. We showed as expected that liquids with the smallest ratio of carbon versus hydrogen in their molecular formula present the best restoration property after an electrical arc, property that is crucial for liquids impregnating metallized capacitors