Root cause analysis of red color band appeared on multi core MV XLPE insulation

Indian cable manufacturers came across a unique problem of red coloration of natural insulation in medium voltage (MV) multi core crosslinked polyethylene (XLPE) cables. The color appeared sporadically and sparingly in few cables, in spiral form during testing or laying operation, when insulation exposed to atmospheric condition. An initiative had taken to conduct the root cause analysis and fix the problem. With series of spectroscopic testing and simulative studies, it was identified that the sources of color bands were organic Nitrogen based compounds in different isomers. These compounds changed forms in presence of light, heat and moisture to generate color (yellow to pink to red) without interacting with insulation. Laboratory simulative tests were done and source was found to be bad polyvinyl chloride (PVC) fillers which were used in multi core cables. The studies continued on bad fillers and identified similar organic materials. The phenomenon was not observed in single core and multi core cable with non PVC fillers. Although not all PVC fillers were found to cause similar problem or contain the nitro compounds, it can be thought provoking to look for good PVC fillers or non PVC fillers for multi core MV cables.