Determination of threshold and maximum operating electric stresses for selected high-voltage insulations

Tests were initiated to establish the maximum safe operating electric stresses of crosslinked polyethylene insulated cables having contaminants in the insulation. The use of a range of sizes and levels of contaminants in the insulation to obtain cables with a range of dielectric breakdown strengths was investigated. Based on the preliminary results, a selection was made to achieve cables with the range of breakdown strength required for the study. After the selection was completed two sizes of contaminants were selected to manufacture cables with medium and low breakdown strength. High breakdown strength was achieved by using cables without contaminants in the insulation. Using the newly manufactured cables (after subjecting to a thermal treatment) and a test method developed during the previous research project numerous tests were performed and the threshold voltage level of the three cables was determined at room temperature.