Understanding surface degradation on polymeric insulators using rotating wheel and dip test under DC stress

Abstract

In the present work, surface degradation studies are performed on silicone rubber based polymeric insulators using rotating wheel and dip test under DC voltage application. This work gains importance as number of HVDC lines are being constructed for transferring bulk power over long distances particularly in the country. A newly developed rotating wheel and dip test arrangement is used for the study; provision is made in the experimental set up to apply two different contaminants simulating different environmental conditions simultaneously. In one tank standard contaminant NH 4 Cl as per IEC 62217/IEC TR 62730 is used and in other tank acidic contaminant is used to simulate normal and acidic rain conditions. A comparative study is conducted on the insulator specimen under different environmental stresses to evaluate long term performance. The conductivity of both normal and acidic contaminants is kept 2.5 mS/cm approximately to observe the effect of acidic environment on long term performance. During the experimental duration of 1000 hours leakage current was regularly measured and recorded. Samples were visually investigated and degradation was found to be more under acidic environment and tracking was observed. After the experiment, physico-chemical analysis is conducted on the degraded samples. Fourier transform infrared (FTIR) spectroscopy is utilized to analyze the surface chemical changes on degraded insulators samples. Salt deposition was detected on aged samples in the FTIR spectrum. Scanning Electron Microscopy (SEM) and Energy Dispersive X-Ray Analysis (EDAX) were conducted to detect elemental presence over the surface of degraded/aged samples. Thermo-Gravimetric Analysis (TGA) is utilized to analyze thermal stability and loss of ATH fillers before and after aging experiment.