DC CONDUCTION AND DISCHARGE ACTIVITY IN HYDROCARBON OILS SUBJECTED TOREDUCED PRESSURE

The effect of reduced pressure on the DC quasi-steady state and discha rge activity in hydrocarbon oils has been studied experimentally. Nonu niform high DC field is applied to fresh and aged transformer oil and liquid paraffin sample. The applied pressure is reduced from about 133 to 6.6 kPa and then increased vice versa for each applied voltage ins ide a controlled vacuum chamber. At a fixed voltage level the quasi st eady state current is found to remain almost unchanged with pressure r eduction down to a certain critical sub-atmospheric pressure, where af ter the current behavior is different for different oils. It increases or decreases sharply for transformer oil and liquid paraffin respecti vely. The value of this critical pressure increases as the applied vol tage is increased. Reduction of pressure has similar effects on discha rge activity as well. The experimental results suggest that vaporizati on and molecular structure of oils play an important role at sub-atmos pheric pressure.