Numerical investigation of temperature and electric field dynamics in polymer insulation at HVDC

At sufficiently high DC electric field in polymer insulation breakdown will occur due to heating. The current that passes through the insulation depends on the electric field, the temperature, and the composition. The associated temperature rise depends on the thickness of the insulation layer and the thermal boundary conditions. A numerical model has been used to study the temperature and electric field dynamics at ramp tests of flat insulation layers. The average electric fields at thermal breakdown have been evaluated for different insulation thicknesses and thermal boundary conditions. The thermal breakdown field can be twice as high for a 0.1 mm well cooled insulation sample as compared to a 10 mm thick sample that is naturally cooled, and the thermal breakdown field increases with increasing ramp rate.