Research On Detection Method Of Local Discharge Optical Fiber Sensing For Typical Insulating Media Of Power Cable

Partial discharge is an important manifestation of insulation faults in cables.Online monitoring of cables and timely detection of partial discharge within the cables are of significant importance for ensuring normal cable operation.Compared to traditional methods of partial discharge detection,optical fiber sensing technology,as one of the non-electrical measurement methods for detecting partial discharge,offers unique advantages such as compact size,excellent insulation performance,strong resistance to electromagnetic interference,and good reusability.It provides a new approach for online detection of partial discharge.In this study,the distributed feedback fiber laser(DFB-FL)is chosen as the research object.Based on the working principle and acoustic coupling method of the DFB-FL sensor,a fiber optic sensing detection system based on DFB-FL is designed.A sound and image joint detection platform for solid dielectric electrical treeing is constructed to detect cross-linked polyethylene(XLPE)commonly used in power cables and ethylene propylene rubber in cable accessories.By analyzing the growth pattern of electrical treeing,the relationship between different growth stages of electrical treeing and ultrasonic waves generated by partial discharge is studied.The feasibility of the DFB-FL fiber optic detection system for solid dielectric partial discharge detection is validated.Frequency domain analysis of the DFB-FL detection signal is conducted to investigate the source of noise in the signal and preliminarily analyze the frequency distribution characteristics of partial discharge in solid dielectrics.A 220 k V cross-linked polyethylene cable model is established using multi-physics finite element simulation.The propagation attenuation law of ultrasonic waves in the cable is analyzed,and it is determined that the multi-layer structure of the cable body is the main factor causing significant attenuation of the acoustic signal.A partial discharge detection platform for the cable’s physical model is constructed to simulate the partial discharge process.By comparing the detection results of the DFB-FL sensor placed at different positions,distances,and angles,it is found that the DFB-FL sensor is most sensitive when positioned directly in front of the partial discharge source.The peak-to-peak value of the signal exponentially decays with the increase of distance.The DFB-FL sensor is more sensitive when placed longitudinally along the cable.The experimental results are in good agreement with the simulation results.By comparing the experimental results obtained from the digital partial discharge detector and the DFB-FL system,it is observed that there is a positive correlation between the amount of partial discharge and the peak-to-peak value of the ultrasonic signal under the same voltage level.At different voltage levels,higher voltages correspond to larger amounts of partial discharge,wider discharge phase ranges,and more ultrasonic signals.The DFB-FL detection system can detect ultrasonic signals generated by partial discharge with a minimum discharge amount of 58 p C,indicating its high sensitivity.