A Novel Online Monitoring Scheme for Underground Power Cable Insulation Based on Common-Mode Leakage Current Measurement

Insulation aging of underground power cables may lead to severe fault and system outages. Condition monitoring of cable insulation is essential to maintain power system reliability. However, most existing insulation monitoring methods can only work in offline mode and cannot describe cable aging severity quantitatively. In this article, a novel online monitoring scheme for underground power cable insulation based on common-mode (CM) leakage current measurement is proposed. An online neutral-point voltage injection approach is proposed, and CM leakage current distribution model for both the cables with and without metal sheath under the injected voltage is derived. The insulation capacitance can therefore be monitored online without disturbance to the system operation. Simulations and experiments are conducted to prove the effectiveness of the proposed method. With the aid of a designed CM leakage current sensor, CM leakage current smaller than 5 mA can be detected and the accurate evaluation of aging severity is achieved. The key feature of the proposed method lies in its nonintrusiveness and online fashion: the normal operation of the system will not be interrupted, and accurate quantitative monitoring of cable insulation can be achieved online.