Research On Detection And Location Methods Of Water Trees In Polymer Insulated Cable

Crosslinked polyethylene(XLPE)cables are widely used in power distribution systems due to their excellent performance.However,water tree aging may occur in the insulation of power cables due to factors such as moisture,electric field,which may cause local electric field strengthening,reduce cable insulation performance,and develop into electric trees that can cause short circuit accidents,affecting the stable operation of power systems.Monitoring power cable insulation is essential to prevent water tree aging,and developing a nondestructive and convenient diagnostic method can help extend the service life of cables and reduce the accident rate,which is of great significance to the power industry and society.The time domain reflectometry(TDR)is a simple and efficient cable detection method with wide application in fault and length measurement of cables.However,there are uncertainties in the detection of water tree aging.In this paper,a study on the reflection characteristics of water tree detection by the time domain reflectometry method based on transmission line theory is conducted.A time domain dual-interface resolution model is established,based on the transmission line theory and the coaxial cable equivalent dielectric constant method proposed based on the circuit principle,which can resolve and predict the reflection characteristics of the water tree segment of the cable.The propagation characteristics of high-frequency signals in the cable are also studied to analyze the signal requirements of the TDR method for cable water tree detection.Based on the dual-interface model and high-frequency propagation characteristics,a method to improve the positioning accuracy of the time domain reflectometry method is analyzed.The analytical model is validated using finite element simulation software to further study the experiments and reflection characteristics.The results of the analytical model are in good agreement with the finite element results,taking into account the effects of water content in the water tree area,axial length of the water tree section,and the conductivity of the water tree.Simulations are conducted to investigate the localization accuracy of the time domain reflectometry method,the effect of the water tree conductivity size,and whether the water tree is penetrated on the reflected wave,as well as the effect of the detection signal on the reflected wave.Finally,TDR experiments are conducted on a simulated water tree of 10 k V cable to further verify the effectiveness of the analytical model.The results show that the simulated water tree reflections are similar to the analytical results and the variation pattern is consistent,taking into account the number of water trees,the length of water tree segments,and the conductivity of water trees.