Research On Magnetic Leakage Detection And Defect Identification For Broken Steel Strand Of Transmission Lines

By the aeolian vibration,rain-wind vibration and galloping caused by ice shedding in freezing rain climate,overhead transmission lines damage and even broken steel strands always occur unavoidably.The presence of the outer aluminum strands presents a significant obstacle for researchers to monitor the internal condition of transmission lines,especially Aluminum Conductor Steel Reinforced.Therefore,the investigation of leakage detection and defect identification methods for broken steel strand in ACSR conductor has important engineering value for transmission line operation and maintenance.Firstly,the similarities and differences between ACSR conductor and SWR leakage field distribution are compared and analyzed by theoretical derivation and Ansoft Maxwell finite element calculation.It is found that the ACSR defect leakage magnetic field exhibits low intensity,strong spatial dispersion,weak lifting-off effect and relatively uniform circumferential distribution under the interference of the aluminum strand layer.Based on the non-permeability of aluminum,a steel-air composite layer model is proposed instead of ACSR conductor for finite element calculation,which ensures the simulation accuracy at the same time reduces the computational cost.Secondly,the effects of the circuit form and key dimensional parameters such as pole spacing L,radial air gap δ,and lift-off value Δf on the magnetization effect of ACSR are analyzed using finite element simulation.Research shows that the double-loop structure can effectively improve the magnetization intensity of the parts to be tested with better magnetization uniformity.In addition,the graph of excitation structure parameters-magnetization intensity in a certain range is obtained,which provides a theoretical basis for the structural design of excitation devices.Thirdly,Ansoft Maxwell is used to simulate the ACSR conductor with different parameters of broken steel strands,and a leakage magnetic experiment platform is built to verify it.The experimental data are further visualized based on the leakage imaging theory.The basic morphology of the leakage magnetic signal under different defect parameters is acquired.And relationship curve between defect parameters of the broken strand and the leakage signal amplitude is obtained,as well as the mathematical relationship between them is initially established.Finally,he research is carried out for the broken strand defect recognition method,and the image recognition method based on Compressed Sensing wavelet filtering is applied to ACSR conductor leakage signal,discovering that the method has low identification accuracy and certain restrictions for ACSR conductor defect identification.Therefore,a new idea of using single channel time-frequency analysis for broken strand identification is proposed.It is shown that the method has higher accuracy in identifying the ACSR conductor fracture width and the number of broken steel strands compared to the image processing method with multi-channel leakage data fusion.With the improved method,the detection error of the fracture width is less than 2 mm,and the accuracy of the number of broken strands can reach 91.67%.