Integrated Fiber Optic Distributed Sensors for Bi-Modal Fault Detection and Dynamic Cable Rating

The growth in renewable energy and the inherent distributed nature of these sources is challenging the electric grid, calling for modernization to a more intelligent, reconfigurable distribution system. It is well understood that with greater use of distributed energy sources, which can result in significant- even reverse power flows, smart protective relaying technologies become essential for safe and reliable grid operation. The proposed project will demonstrate a bi-modal fiber optic distributed temperature and acoustic sensor for monitoring both parameters in high voltage distribution cables. This will allow fast detection and location of ground faults, and real-time monitoring of cable conductor temperature to assess dynamic cable rating- critical information for smart protective relaying to enhance grid resiliency and power restoration in the event of a supply interruption. When incorporated within power cable sheathing, the all di-electric construction of optical fibers has no impact on performance of these cables while allowing direct measurement of the conductor with no interference. This project will demonstrate a bimodal distributed temperature and acoustic sensor capable of complete monitoring of these parameters over the entire length of cable. An optical test cable incorporating a pair of conventional telecommunications-grade fibers will be used for the project demonstration, and available for any “live” high-voltage cable tests. A commercial Raman-scatter type distributed temperature instrument will be used to monitor cable/conductor temperature. Such fiber optic sensors have been demonstrated in this application with good results, however the measurement time is not adequate to quickly detect rapid thermal events or mechanical disturbances associated with ground faults. The main development of this project will be a distributed acoustic/vibration sensor capable of almost instantaneous detection and location of disturbances acting on the cable due to ground faults. This sensor detects sudden changes in light propagation in the sensor fiber and applies a fast auto-correlation method to determine its location. The proposed bimodal sensor will deliver critical information for advanced protective relaying control systems, providing real-time intelligence at the physical layer of the grid. The high-speed disturbance sensor innovation has other commercial applications in physical security, pipeline monitoring, and transportation infrastructure safety and integrity.