Research On Detection Of 10kV XLPE Cable Insulation Defect Based On Oscillatory Voltage Method

XLPE cable has been widely applied in power supply and distribution lines of major cities,and its safety is directly related to the reliability of power supply.Because of the complex operation environment of cable and the insulation defects during installation,it often causes operation failures and latent failures.Partial discharge(PD)signal is an important characterization parameter of cable insulation state,which contains rich information about cable insulation defects.Therefore,effective detection of partial discharge in cable insulation defects has become the key to reduce cable failure rate.In recent years,the partial discharge detection technology based on oscillating wave voltage method has been widely promoted with its own advantages.In order to prove the effectiveness of the oscillatory wave voltage method in detecting the partial discharge of 10 k V XLPE power cable,this paper first analyzes the fault causes of 10 k V XLPE power cable,and selectes three kinds of insulation defects of power cable,including the main insulation with air gap,the terminal with the scratch,and the joint with impurity,as the research objects.Three typical cable defect models are established by using the finite element electric field simulation software ANSOFT/Maxwell.The initial discharge field strength of each defect is calculated according to the empirical formula and the size parameters of the model.The initial voltage of the partial discharge of the three defects under the oscillating wave voltage is calculated by the finite element electric field simulation,which lays the foundation for the follow-up study.In order to suppress the white noise and periodic narrowband interference signals which are infiltrated in the electric power cable partial discharge detection,a high order partial differential equation(PDE)algorithm is used to denoise the low frequency subsignal after wavelet decomposition on the basis of the wavelet transform preprocessing and post processing.At the same time,signal to noise ratio(SNR)is selected as the criterion of iterative termination in the process of iteration.MATLAB is used to denoise the simulated PD signal with noise,and the simulation results of the traditional wavelet threshold denoising method are compared and analyzed to verify the effectiveness of the improved interference suppression method.According to the detection principle of XLPE Cable Partial Discharge by oscillatory wave voltage method,a model of oscillating wave test system(OWTS)is built based on MATLAB Simulink.Experiments are conducted on three kinds of XLPE cable defects under oscillating wave voltage.It is proved that the main defect of 10 k V XLPE cable can be detected effectively by oscillating wave voltage method.At the same time,the feasibility of calculating the initial voltage of PD by finite element electric field simulation is proved by comparing the initial discharge voltage calculated by the oscillating wave experiment and the electric field simulation.