Surface breakdown test results of mineral oil and silicone oil with Kraft paper and Nomex

The authors describe a high-voltage test procedure for investigating surface breakdown and report on its application. A high-voltage test vessel was constructed and a test procedure developed to explore the solid/fluid interface. Both silicone oil and mineral oil were tested. Kraft paper boards and Nomex boards were the solid materials investigated. Average breakdown voltages from measurements on all boards are tabulated. Results show that both oils performed similarly, particularly on low-density boards. Permittivity matching appears to be a factor in the dielectric strength of the interface under impulse voltages. However, for AC voltages, poor resistance to partial discharges may dominate this effect. Electrical breakdowns under positive impulse voltages were generally lower than under negative impulse voltages