Research On Fiber Optic Sensing And Positioning Of Ultrasonic Signals Of Cable Partial Discharge

Power cable is an important power equipment for the normal operation of power network.In the process of cable and accessory power transmission,under the action of DC electric field for a long time,the space charge accumulation will cause partial discharge field in the dielectric,and then cause partial discharge.Real-time monitoring of partial discharge of power cable can effectively grasp the running state of the cable,which is the basic requirement to ensure the safe operation of the power grid.At present,researchers at home and abroad have put forward many methods for cable PD detection,but there is a lack of effective experimental means for long-distance HVDC cable PD detection.According to the above research background,based on the characteristics of Sagnac fiber optic sensor,such as high precision,easy operation,on-line real-time monitoring and no influence on the normal operation of cable,etc,in this paper,optical fiber sensor is used to detect and locate the ultrasonic partial discharge signal of long-distance high-voltage cable.Firstly,the mechanism of PD in cable and the ultrasonic characteristics of PD detected by optical fiber are analyzed,and the principle of distributed optical fiber sensing light path,phase and polarization state are studied.In order to make the signals in the detection system show completely,the synchronous demodulation method of optical fiber sensing for detecting partial discharge in long-distance cable is adopted.Secondly,an improved polarization control algorithm based on adaptive distance estimation is proposed to solve the polarization degradation problem in Sagnac fiber sensor,the performance indexes of the improved algorithm,such as noise amplitude,control precision and attenuation rate,are simulated and compared with MATLAB software.The simulation results show that the improved algorithm converges to the target polarization state more quickly than the original algorithm,and the control accuracy reaches 10^-4when the noise amplitudeγ=0.07,the output signal sensitivity and positioning precision of the optical fiber sensing detection system are improved,and the accuracy of the optical fiber detecting partial discharge signal is guaranteed.Finally,based on distributed Sagnac sensing fiber,the location algorithm of partial discharge in long-distance power cable is studied.The linear and double loop Sagnac optical fiber sensing systems are designed to detect partial discharge in long distance cables.The method of double-loop sensor detection and location is improved,and the partial discharge points are obtained by time delay estimation algorithm and cross-correlation operation.The key device of the experiment is selected,the experimental platform is set up in the laboratory and in the field,and the partial discharge signal of the cable is collected.The experiment shows that the positioning error of±320 k V cable partial discharge is smaller than that of the straight line,and the positioning accuracy of the dual-loop detection system is up to±80 m for the PD signal of 6 km long cable.