Prebreakdown events in dielectric liquids

A charge-storage technique has been used to enable the transient current flow in hexane, using a point-cathode plane-anode system, to be deduced. A spark-in-air light source has enabled the optical state of the stressed liquid to be studied. Following the application of a step voltage, the current is observed to increase rapidly to a peak value and subsequently to decay. Conditioning effects and a charge-decay phenomenon have also been recorded. The current/time curves have been interpreted in terms of charge injection at the cathode, where the Laplacian field is enhanced by the drift of positive charge present in the bulk of the liquid. The effect of the conditioning is to impede this charge injection. Breakdown is similarly interpreted in terms of energy input, suggesting that breakdown in the liquid is a thermally initiated event. The first appearence of a low-density discharge region at the cathode is associated with an energy input not greater than 10¿8 J.