Partial discharge behaviour of cross-linked polyethylene - natural rubber blends nanocomposites as electrical insulating material

Abstract

Polymeric materials are widely used in power apparatus as electrical insulation, especially for high voltage cable insulation. However, partial discharge (PD) has always been a predecessor to major faults and problems in this field. By adding a weight percentage (wt%) of a nanofiller to the electrical insulation, the physical and electrical properties can be enhanced. In this research, natural rubber (NR) blends polymeric material of cross-linked polyethylene (XLPE) as insulation was combined with nanofillers, namely nanosilica (SiO2) or organo-montmorillonite (O-MMT). Seven samples comprising six compositions of a blend of 20 wt% NR and 80 wt% of XLPE with 2, 4, and 8 pph from SiO2 and O-MMT, and one without nanofiller were used in the experiments. Two PD tests were carried out based on CIGRE Method II technique, where 7 kVrms high voltage was applied for 1 hour and 3 hours. LabVIEW™ program was used to analyse the PD data captured from the on-line and off-line PD measuring system where PD pulse magnitudes and number of PD occurrences were measured. Results showed that samples of NR-XLPE blended with SiO2 have lower PD number than the O-MMT samples. Scanning Electron Microscopy images showed that smoother surfaces were observed as the wt% of the nanofiller increased, indicating that the samples were less degraded. Energy Dispersive X-ray measurement of samples containing SiO2 emitted more stable amounts of oxygen and carbon contents when exposed to high voltage. Analysis on Fourier Transform Infrared spectroscopy showed a reduction of OH groups in the samples. Using QuickField™, the electric field distribution of the samples confirmed that in series of 2, 4, and 8 pph nanofiller loading, there is a correlation between the amount of nanofiller and discharge activities. The findings have shown that SiO2 and O-MMT and the different loadings do enhance the insulation properties when mixed with NR-XLPE.