DC field effects on streaming electrification in insulating oils

Electrification in insulating liquids in a paper-pressboard tube model with concentric cylindrical electrode geometry under an external DC field effect has been investigated. Energization by positive DC voltage (field acting radially outwards) always enhanced the streaming electrification; however, when the applied voltage was negative, (field acting radially inwards) a polarity reversal in streaming current has been observed. Flow rate did not have any influence on the zero cross over point (the field at which current crossed the zero value); however, the additive concentration, moisture content and the temperature affected this zero cross over point. The conduction currents corresponding to fields where streaming currents were zero were also relatively low, hence it is possible use this technique to keep the streaming current close to zero by doping the oil with proper concentrations of carbazole and applying a DC negative field