Study on the performance of underground XLPE cables in service based on tan delta and capacitance measurements

Performance of underground XLPE cables in service is critical because of ageing mechanisms influences. One of the techniques to evaluate performance of aged and unaged underground XLPE cables is based on tan delta and capacitance measurements of the cable insulations. This study focuses on underground XLPE cables which rated at 11 kV and 22 kV for both 1-core and 3-core types. Tan delta and capacitance data of underground XLPE cables are obtained using a Schering bridge instrument. Tan delta and capacitance measurements are performed at ambient temperature (about 27degC) and 50 Hz power frequency. The analysis of data show that tan delta values increased in proportion to the aging time of the cables. Meanwhile the data analysis of the capacitance measurement shows that the values of capacitance inconsistent. Nevertheless, tan delta measurement is more accurate and appropriate parameter for evaluating performance of underground XLPE cables as compared to capacitance parameter. Therefore, the finding of this study shows that aging mechanisms contributes the deteriorations of underground XLPE cable insulations in service and consequently the value of tan delta increases with aging time of the cables.