Effect of Ambient Gas on ARC Initiation Characteristics in Soil

The electrical breakdown characteristics of soil were measured with the test sample in air and then with the air in the soil voids replaced with SF6. All of the measured breakdown properties that are associated with arc initiation, such as threshold field and energy to breakdown, were consistently different for air and SF6. The ratios of these quantities are comparable to the ratio of the breakdown electric-field strengths of free air and SF6 at one atmosphere. This agreement between the breakdown strengths of soil and free gases is strong evidence that the initiation of arc breakdowns in soil involves ionization of the air in the voids between the soil particles.