Correlation Between Polarization Mechanisms and Material Characteristics in Thermally Aged 320 kV HVDC Cable Insulation

• Published in: IEEE transactions on dielectrics and electrical insulation p. 1
• Main Authors: Borthakur, Darshan Prakash, Verma, Alok Ranjan
• Format: Journal Article
• Language: English
• Published: IEEE 10-07-2024
• Subjects: Aging; Cross-linked Polyethylene (XLPE); Current measurement; Dielectric measurement; Frequency measurement; HVDC Cable; Mathematical models; Physicochemical Analyses; Polarization and Depolarization Currents; Relaxation Frequency Distribution (RFD); Thermal degradation; Time Domain Measurements; X-ray scattering
• ISSN: 1070-9878; 1558-4135
• DOI: 10.1109/TDEI.2024.3426492

In the present work, degradation analysis associated with the thermal stress in a 320 kV Cross-linked Polyethylene (XLPE) insulated cable insulation has been carried out. Accelerated thermal ageing at 140 °C for 30 days is done for XLPE insulation to understand the material degradation. Physicochemical analyses such as Fourier Transform Infrared (FTIR) Spectroscopy, Differential Scanning Calorimetry (DSC), X-Ray Diffraction (XRD) analyses have been performed to understand the material degradation due to thermal stress. These material investigations show interesting features regarding changes in characteristic peaks and formation of carbonyl group, micro-structural changes and decreased degree of crystallinity with thermal ageing as evident by FTIR, XRD and DSC respectively. Measurement of Polarization and Depolarization Current (PDC) have been carried out in the thermally aged insulation samples. It is observed that with thermal ageing the polarization and depolarization current magnitude seem to increase. A novel technique employing Relaxation Frequency Distribution (RFD) has been used to get a deeper insight into the thermal degradation of the material by understanding the relaxation mechanism of the dipoles with the thermal ageing. RFD spectrum shows a dominant slow polarization as the material undergoes thermal ageing. Higher dielectric loss with thermal ageing of the samples has been observed from the RFD spectrum.This higher dielectric loss is also validated using Dielectric Dissipation Factor (tanδ) measurement. Moreover, a correlation between RFD spectrum and physicochemical analyses has been established.