Insulation ageing

摘要

Electric cables with organic polymer insulations have a useful design life span under specific conditions. One main cause of polymer degradation is polymer chain scission. This happens when free radicals from within or outside of the cable insulation cause breakages in the polymer backbone chain over time. This is a natural process, accelerated by heat, moisture, light, radiation and mechanical stressors. It results in degradation of mechanical performance and the multiple processes combine to increase the number of carriers in the polymer insulation material, thereby increasing conduction and ultimately leading to dielectric breakdown. The effects of polymer ageing can be seen as both physical and electrical changes in the material properties, like reduced flexibility, deterioration of the materials' elongation at break, hardening, cracking, surface chalking, discolouration and decreasing dielectric performance. Other operational properties may also be affected, including insulation resistance, flame retardance and oil/water resistance.