Study on the Incipient Fault Development Process and HFCT Characteristics of Cable Intermediate Joint Interface in Waterlogged Environment

Moisture at the interface between the cross-linked polyethylene (XLPE) insulation and the silicone rubber (SiR) in the intermediate joint is one of the main causes of surface flashover in cable intermediate joints. However, research on the incipient fault caused by moisture at the intermediate joint interface is currently limited. This paper conducts incipient fault experiments on 10 kV cable intermediate joints exposed to moisture in a waterlogged environment. Based on power frequency voltage and current detection, a high-frequency current (HFCT) detection method is introduced to extract characteristic information, such as pulse amplitude and discharge frequency, at different stages of incipient fault development. The results show that the development process of the incipient fault at cable intermediate joints can be divided into three stages: initial, middle, and late stages. In the initial stage, the fault current amplitude is quite small, approximately 10–20 mA, and the high-frequency pulses are sparse and low in amplitude. In the middle stage, the fault current amplitude increases to 300 mA-850 mA, and the high-frequency pulse amplitude and frequency increase significantly. In the late stage, the fault current, high-frequency pulse amplitude, and discharge frequency all increase slightly compared to the middle stage. This research finding can provide a reference for early warning of distribution cable line faults.