Dynamic Resistance Characteristics of an Incipient Fault of a Medium-Voltage Cable Joint in a Water-Logged Environment

The internal flashover of a medium-voltage cable joint in a water-logged environment seriously affects the reliability of distribution networks. Monitoring an Incipient Fault can help prevent a power failure caused by a permanent fault; however, there have been few studies of the development and characteristics of the Incipient Fault. In this study, we experimentally simulated an Incipient Fault in a medium-voltage cable joint in a water-logged environment according to actual operating scenarios, and measured both nonelectrical characteristics, namely insulation erosion, displacement, and deformation of water electrode, and electrical characteristics, namely current and resistance changes, during the fault process. The results showed that the Incipient Fault underwent long-term accumulation, while its short-term characteristics did not change considerably. The fault resistance characteristic was made up of a water electrode, the erosion trace, and arc resistance in series, and fault characteristics were little affected by the external circuit like a transmission line. Then, we selected two typical scenarios in which the first fault and erosion trace penetrated the insulation and analyzed the time-domain characteristics of the magnitude and variation of the resistance values of the water, erosion trace, and arc in the Incipient Fault. The results showed that arc resistance played a major role in the fault current at the beginning and end of the fault, and water played a major role in the middle stage. During the fault process, the current amplitude showed the following trend: rising—small fluctuations—falling. As fault damage accumulated, the influence of erosion traces on the fault characteristics became larger. When the erosion traces penetrated the insulation surface, a permanent fault would be caused.