PREBREAKDOWN CURRENTS IN WATER AND AQUEOUS-SOLUTIONS AND THEIR INFLUENCE ON PULSED DIELECTRIC-BREAKDOWN

The-current response of water and sodium chloride solutions subjected to high amplitude electric fields of sub-microsecond duration has been investigated. The prebreakdown current-voltage relationship for these liquids is found to be nearly linear for the fields considered and th erefore described by a resistance, R. For constant concentration, R do es not extrapolate to zero as the gap width, d, goes to zero, suggesti ng the presence of a high resistivity sheath near the electrodes. Esti mates for the sheath parameters (electric held in the sheath, E(s), wi dth, d(l), formation time, t(l), and ion density, n(s)) are obtained f rom these measurements. The contribution of electronic and ionic curre nts to the breakdown probability has been assessed from the power inpu t to the liquid during the pre-breakdown phase. For applied fields wit h sub-microsecond duration, the input power is primarily due to electr on field emission currents whose magnitude is a function of the field in the ionic sheath. For the parameters investigated, ionic currents a re found to play a secondary role in these time scales. (C) 1995 Ameri can Institute of Physics.