Assessment of medium voltage underground cable incipient fault severity in effectively grounded system based on Volt-Ampere characteristic

Underground cable incipient faults, which are originally self-clearing, may repeatedly occur and gradually develop into permanent faults. The detection and assessment of these faults are crucial tasks in fault anticipation and predictive maintenance. However, while extensive research has been conducted on incipient fault detection and identification, the quantitative assessment of fault severity remains a significant gap in existing literature. To address this, this paper proposes a novel dynamic incipient fault model that explicitly incorporates the carbonization path evolution driven by arc combustion. This model reveals that the carbonization degree is the key physical indicator of severity, as recurring faults produce carbonization compounds that reduce the equivalent resistance. Moreover, the carbonization degree is shown to distinctly modify the Volt-Ampere (V-A) characteristics of the arcing fault. Consequently, a quantitative severity assessment method based on V-A characteristics is established to track the dynamic fault development process. The proposed method is verified by PSCAD/EMTDC simulations, and its effectiveness is further validated through extensive laboratory experiments and field measured data.