Breakpoint and Moisture Detection Method Based on Distributed Brillouin Optical Fiber Built in Buffer Layer of High-Voltage XLPE Cable

In recent years, the water-blocking tape in high-voltage (HV) crosslinked polyethylene (XLPE) cable has suffered from penetrating moisture frequently, which affects its safe and stable operation, while there are no effective detection methods yet. In this article, a 110 kV cable sample was prepared, with a single-mode fiber of 30 m built in it. Meanwhile, a distributed detection system for built-in optical fiber of 110 kV cable was established and the criterion for Brillouin optical time domain reflectometry (BOTDR) breakpoint detection method was proposed. The comparison test of breakpoint detection methods for built-in optical fiber was carried out using BOTDR and optical time domain reflectometry (OTDR). Besides, detection tests of moisture water blocking tape including its drying process were launched using BOTDR. The relationship of Brillouin frequency shift (BFS) with moisture length, position, and drying process of the tape was studied. The results have demonstrated that BOTDR plays a better role in detecting breakpoint with poor-quality end face than OTDR. By using BOTDR to detect moisture tape in cable, the BFS decreases sharply when moisture length over some thresholds and linearly falls with increasing moisture length. As time passes, the BFS gradually increases, which can characterize drying process.