High Temperature Insulation Materials for DC Cable Insulation - Part III: Degradation and Surface Breakdown

The first two parts in this series gave full analysis and discussion of five high temperature insulation materials, i.e. PTFE, FEP, ETFE, PEEK, and PI over aspects of space charge behavior, conduction property as well as partial discharge, respectively. In this part, the degradation and surface breakdown properties are investigated and the related mechanism is discussed. The results showed that due to stable formation of C-F structures, PTFE and FEP melted locally during arc erosion test, with no carbon element being precipitated. At 25 degrees C, PI showed the best surface anti-arc erosion property among ETFE, PEEK and PI. However, compared with other samples, the arc withstand property of PI can be much more influenced at higher temperature and in case of surface contamination. Compared with the results measured at 25 degrees C, the surface flashover voltage decreased for all samples when measured at 150 degrees C, which can be explained by the expansion of "analogous ineffective region". FEP has the highest surface flashover voltage at both 25 degrees C and 150 degrees C, which is due to higher surface roughness. The content of this paper provides a reference for aging characterization and evaluation of high temperature materials for DC cable and circuit board insulation.