Researchers from South Africa have developed a groundbreaking and reliable method for the non-destructive testing (NDT) of cross-linked polyethylene (XLPE) insulated power cables. This innovation offers a critical solution for assessing the long-term integrity of vital underground infrastructure, which typically operates for decades under fluctuating environmental and load conditions.
Currently, many countries rely on a destructive testing paradigm for XLPE cables, involving the cutting and high-voltage testing of samples. While effective at identifying defects such as "water trees"—microscopic moisture-induced branches in the insulation—this approach is inherently expensive and impractical, as the cable becomes unusable after testing.
To address these limitations, scientists from the Vaal University of Technology of South Africa undertook a comprehensive study to validate a non-destructive alternative. Their research involved subjecting identical 10-meter sections of XLPE cable to an accelerated aging process, simulating years of operational wear. At regular intervals, the cables underwent three distinct types of non-destructive measurements: Tan δ, IRC, and RVM.
The Tan δ (tangent of the dielectric loss angle) method provided a rapid assessment of the cable insulation's overall condition. This technique measures energy losses within the insulation, indicating the degree of wear or micro-damage, and serves as a vital tool for immediate primary testing.
The IRC (isothermal relaxation current) method offered deeper insights into the severity and internal damage of the insulation. By measuring the decaying current of charges released from micro-defects or "traps" after voltage removal, this technique elucidated the nature and depth of internal structural changes due to aging.
Lastly, the RVM (reverse voltage measurement) method accurately determined the quantity of residual charges and the extent of moisture saturation within the insulation. By analyzing the "reverse voltage" that reappears after controlled charging and discharging, this method proved particularly valuable for detecting moisture penetration, a primary factor in cable degradation.
The combined application of these three non-destructive methods yielded a comprehensive and objective picture of cable degradation. The results consistently demonstrated predictable changes across all parameters as aging progressed, with increasing losses, trapped charges, and moisture ingress. The consistency and coherence of these findings across all three NDT techniques unequivocally validate the reliability of this complex of non-destructive measurements for assessing XLPE cable condition.
This innovative approach paves the way for regular and safe testing of underground power cables without the need for disconnection or physical damage. This is particularly crucial for extensive and difficult-to-access sections of backbone networks. In practice, this means energy companies will gain the unprecedented ability to monitor the condition of cable lines in a timely and accurate manner, foregoing costly and destructive tests. Such proactive monitoring will enable the early identification of wear and hidden defects, substantially reducing the risk of accidents, power outages, and emergency repairs, while simultaneously optimizing critical infrastructure replacement and maintenance schedules.
