Electrical and material test of 200 kV HVDC XLPE cables after operating for 5 years

The insulation state assessment of two 200 kV HVDC XLPE cables, which have been in operation for 5 years, were performed after a breakdown fault. The electrical test including broadband dielectric spectrum (BDS) test and breakdown strength test. The material test including thermal stimulation current (TSC) test, differential scanning calorimetry (DSC) test, infrared spectrum test, degree of crosslinking test, and thermal elongation ratio test. The results show that the TSC and DSC test can represent the differences due to different breakdown energy between two cables. And the BDS, TSC and DSC test can distinguish between old and new cables. Meanwhile three indicators, including infrared spectrum, degree of crosslinking and thermal elongation ratio test of old cables were even better than new cables.