Insulating Aging Diagnosis And Defect Positioning Of Cross-linking Polyethylene Cable Based On FRA

Crosslinked Polyethylene(XLPE)cable is aging in the long-term operation of electricity,heat,moisture and other factors.Therefore,we need to inquire to detect the operational state of the XLPE cable to achieve effective diagnosis of its operating state.This thesis uses the frequency domain response analysis(FRA)to conduct insulation aging diagnosis and defect positioning.At low frequency,the frequency domain dielectric response can reflect the aging of the cable insulation,and the test of the frequency domain dielectric response will be affected by the excitation amplitude and the semiconductive shielding layer.This thesis uses the system clustering algorithm to extract the characteristic parameters of the degree of insulation of XLPE cables,and establishes a T-S model,changes the test voltage level to analyze the impact of the semi-conductive shielding layer and the excitation amplitude on the frequency domain dielectric response test of cable insulation;At high frequency,the input impedance spectrum of the cable closely correlated with its own distribution parameters,can evaluate the type and severity of cable defects,and further achieve defect positioning,this thesis uses the equivalent circuit model of the XLPE cable to study the frequency of cable parameters,According to the input impedance spectrum of the cable,the characteristic parameter of the type and severity of the cable defect is extracted,and the IFFT algorithm is used to position the defect of the XLPE cable.To study the frequency domain dielectric response of cable insulation under low frequency,this thesis builds XLPE material electric tree aging,water tree aging,thermal aging test platforms,and test system of frequency domain dielectric response,select the XLPE sample in different aging states for frequency domain dielectric response test.This thesis can be seen by analyzing the corresponding frequency domain dielectric response test results: The aging state of the cable insulation can be characterized by the frequency domain dielectric spectrum of the(0.01 ～ 1)Hz band;When the cable is in good condition,the semiconductive shielding layer reduces the loss factor cable insulation,when the cable contains defects,the semiconductive shielding layer increases the loss factor of cable insulation;The excitation amplitude is different,the frequency domain dielectric response of cable insulation is not the same,exhibits nonlinear characteristics,and the deeper the cable insulation,the more obvious nonlinear characteristics.To study the type,severity identification and positioning of cable defects under high frequency,and analyze the factors affecting the positioning accuracy,this thesis simulates the XLPE cable containing different types of defects and test parameters,and according to the simulation test,the cable water tree aging,the heat aging and insulation damage test platform and the input impedance spectrum test system are used,this thesis uses IFFT algorithm to position cable defects,and verifies the simulation results.The test results show that the type and severity of cable defects can be evaluated by feature parameters such as the amplitude,resonance point,resonant cycle,initial phase,and attenuation speed of the cable impedance spectrum;The error of the cable defect positioning is not more than 0.5m with the high-frequency phase spectrum of the cable,and the positioning accuracy is positively correlated with the frequency band width,the sampling frequency interval,and the severity of defects,and it is negatively related to the defect position.This thesis has a certain reference significance for the aging assessment of XLPE cables.