Assessment of Abnormal Aging in AC Three-Phase Cables Based on Apparent Dielectric Loss Factor

As power cables remain in operation for extended periods, their insulation gradually ages, increasing the risk of insulation failure. This paper focuses on the detection and analysis of leakage currents in cable insulation within AC systems by means of a dual current transformer (CT) method. A calculation method based on phase angle normalization is proposed to determine the apparent dielectric loss angle (△δ) and apparent dielectric loss factor (tan△δ), enabling a more accurate assessment of cable aging. Through artificial cable aging tests, it is proven that the tan△δ exhibits more significant changes compared to the actual dielectric loss factor. The former can reach up to 144.73 times the reference value, while the latter is only 10.49 times, demonstrating the rationality and superiority of tan△δ in cable aging assessment. Measurements and analyses of apparent dielectric loss parameters were then conducted on three actual transmission lines with operational durations ranging from 1 to 12 years. The results show that the tan△δ of cables operated for one year is 0.14, while those in service for 10 to 12 years can reach 0.50‒1.40. These findings confirm that the proposed method effectively reflects the aging status of operating power cables. The conclusions of this study provide a new reference for assessing the aging of operating cables.