Abstract
The effect of reduced pressure on the DC quasi-steady state and discharge activity in hydrocarbon oils has been studied experimentally. Nonuniform 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 inside a controlled vacuum chamber.
At a fixed voltage level the quasi steady state current is found to remain almost unchanged with pressure reduction down to a certain critical sub-atmospheric pressure, where after the current behavior is different for different oils. It increases or decreases sharply for transformer oil and liquid paraffin respectively. The value of this critical pressure increases as the applied voltage is increased. Reduction of pressure has similar effects on discharge activity as well. The experimental results suggest that vaporization and molecular structure of oils play an important role at sub-atmospheric pressure.