Study on the molecular structure evolution of long-term-operation XLPE cable insulation materials

Abstract

Crosslinked polyethylene (XLPE) insulation is widely used in power systems because of its excellent properties. During long-term operation, the aging of insulating materials will lead to cable failure and threaten the safe operation of the power system. The molecular structure evolution of XLPE cable insulation materials was studied by Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), differential scanning calorimetry (DSC) and thermogravimetric (TG) methods. The results show that the crystallinity and melting temperature of 0 year sample are the highest, which are 24% and 105.52 °C, respectively. The carbonyl index is small, and the proportion of TG in the first stage is small. After 15 and 30 years of operation, the crystallinity of the cable decreased by 16.7% and 25.0% respectively, the carbonyl index increased first and then slightly decreased, the melting temperature decreased first and then slightly increased, and the proportion of TG in the first stage increased. The results show that the microstructure of the 0 year old sample is relatively complete, and it has good thermal stability and oxidation resistance. After a long period of operation, the crystal region of the sample is destroyed, and the thermal-oxygen reaction takes place, resulting in thermal-oxygen cracking of macromolecules, generating more volatile small molecular groups, and reducing the insulation performance of the cable.