Damage detection in cable braidings using integrated fiber-optic reflectors

In cable industry, structural health monitoring is becoming more and more important. Of special relevance is the damage detection in cables which supply large excavation equipment like bucket wheel excavators in opencast mining. Here, damage localization is often still carried out manually. With a usual cable length of a few kilometers, this method is inefficient and can lead to unnecessary revenue losses caused by long repair and machine downtime. Because of their electromagnetic immunity, their functionality over long transmission distances, their resistance to difficult environmental conditions, and their comparatively easy integrability, fiber optic sensors are particularly suitable for detecting damages in this application. Therefore, in this paper, a novel spatially resolving and inexpensive damage detection system based on fiber optic reflectors is presented. With a physical vapor deposition method, an increased reflectance of the coated single mode fiber ends was achieved. Due to the special integration position of the sensors in the braiding structure of a cable, damage in the jacket area can be detected. Via measurements of the reflected signal intensities, the position of the damage can be resolved over long distances. Furthermore, the sensor arrangement engages only slightly in the manufacturing process of the cable braiding and the cable. The ability of the presented measurement system to perform damage detection independent of the regular power transmission of the cable offers an advantage over standard cable conductor based electrical damage detection techniques.