The Experiment of VLF Tanδ on Service-aged MV Underground Cable

This paper presents the service-aged MV underground cable experiment using very low frequency (VLF) testing. The underground cables in this experiment have been utilized in service for more than 10 years and subjected to TEAM stresses, particularly with moisture, throughout the service time. So, the effect of moisture leads these cables to bad condition. The cables under the experiments are both service-aged and unaged. These cables were prepared the same by peeling both end sides of the cables and were terminated with high voltage insulating tape. The VLF test combined with the tangent delta (tanδ) measurement, according to IEEE Std. 400.2-2013 was performed to assess the condition of these cables and compare them with the unaged cable. The test results revealed that according to IEEE standard 400.2-2013, the service-aged underground cables were assessed in Action Required criteria. Still, the unaged underground cable was assessed in the Further Study Required criteria. Moreover, the tanδ values from service-aged underground cables have significant differences, with service-aged underground cables having higher values than unaged cables. Besides, the variation of tanδ data samples at each test voltage level from some underground cables shows a decreasing trend at 1.0U0 and 1.5U0. Nevertheless, the test voltage at 0.5U0 shows the constant trend of tanδ samples. This analyzed result can indicate that the insulation condition has humidity inside the cable insulation.