Partial Discharge Ultrasonic Detection for Cable Polymer Insulation Using DFB-FL and FBG Collaborative Sensing Technology

Insulation failure is one of the most significant threats to the safety of cable joints. Partial discharge (PD) detection is the most effective method to recognize potential faults in polymer insulation of cable joints. Distributed feedback fiber laser (DFB-FL) acoustic sensing proves highly effective in monitoring partial discharges ultrasonic for liquid insulation. However, the acoustic attenuation in cross-linked polyethylene (XLPE) insulation materials employed for cable joints limits PD ultrasonic propagation to a mere 7-10 cm range. The single point DFB-FL sensing unit is inadequate for detecting PD acoustic signals across mete-length XLPE material of cable joints due to its limited spatial coverage. This paper proposes a novel collaborative sensing method with DFB-FL and Fiber Bragg Grating (FBG), which expands the single point measurement to multiplexing measurement and constructs a dense sensor array to monitor partial discharge signals within cable joint insulation. Meanwhile, a synchronized center wavelength tuning method is presented to compensate for the working-point drift caused by temperature rise during cable joint operation. Then, the DFB-FL/FBG collaborative sensing system is used to detect partial discharge acoustic signals in 110kV XLPE cable insulations. The experiment results demonstrate that DFB-FL/FBG collaborative sensing system can detect acoustic signals generated from PD at 70cm range at 200-300 pC apparent charge. Finally, based on the comparative analysis of different FBG topological structures, the evidence suggests that the serial FBG network structure will reduce signal-to-noise ratio and sensitivity, but parallel-arrayed FBG structure minimally impacts these parameters when combining DFB-FL with multiple FBGs. The hybrid structure combines advantages of both series and parallel structure, enabling larger-area polymer insulation partial discharge acoustic measurement at lower cost.