Space charge development and breakdown in XLPE under DC field

The correlation between space charge accumulation and insulation failure has been investigated in four, polyethylene-based materials subjected to a dc field of 50 kV/mm. Two of the materials tested were equipped with tree-retardant additives. All four materials were aged for extended periods up to 16,000 h. Periodically, the specimens were removed from the external field and subjected to space charge density measurements under no-voltage conditions using the Thermal Step technique. Not a single parameter that would consistently correlate with times to insulation failure could be derived from the space charge measurements. However, the space charge measurements provided valuable insight into a possible link between the dynamics of space charge development and the time of dc aging. In particular, the measurements have shown a consistent surge in the amount of accumulated space charge shortly before insulation breakdown. This phenomenon could be used to screen new materials for dc voltage applications.