Research On Water Tree Growth Characteristics Of XLPE Cable

The water tree aging of cross-linked polyethylene（XLPE）cable is the main reason for the decrease of insulation level and service life of XLPE cable.In order to ensure the safe and reliable long-term operation of XLPE cables and prevent large-scale power outages,it is very important to explore the growth characteristics of water trees in XLPE cables,analyze their aging mechanism,master the initiation law of water tree and explore the growth characteristics of water tree.In this thesis,in order to explore the water tree growth characteristics of XLPE cable under different conditions,different ions,different concentrations,different acid-base environment and different air pressure environment were selected to aging XLPE cable.Based on the improved water needle electrode method,a water tree aging platform for cables under different conditions was constructed and aged.In order to determine the degree of water tree aging in XLPE cables,the growth characteristics of water tree of XLPE cable under different conditions were analyzed from the point of view of the combination of macro dielectric property test and micro morphology detection.In the macroscopic test,polarization-depolarization current method（PDC）is used to test the aged cable under different conditions.Based on the PDC test results,the DC conductivity,0.1Hz dielectric loss factor and aging factor of the cable are calculated.In the aspect of microscopic detection,the cable flake samples were detected by optical microscope,scanning electron microscope（SEM）and infrared spectroscopy（FTIR）.The growth of water branches in the cable was quantitatively analyzed by calculating the growth volume of water tree and the micropore area of water tree channel.Based on the FTIR test results,the water content index is calculated to judge the aging degree of the water tree of the cable,and its accuracy is verified by fitting with the water tree volume.After macroscopic and microscopic tests of cables aged with different ion solutions,it is found that Na⁺and K⁺can promote cable water tree growth,while Cu²⁺and Al³⁺can inhibit cable water tree growth.After macroscopic and microscopic tests of cables aged with different concentrations of solution,it was found that with the increase of solution concentration,the degree of water tree aging of cables showed a trend of first increasing and then decreasing,and the aging degree of water tree is the most serious when the solution concentration is about 2.223mol/L.After the macroscopic and microscopic tests of the cables aged in different acid-base environments,it is found that both acidic and alkaline environments can promote the growth of water trees,and the water branches growing in acidic conditions are larger and more stained than those in alkaline conditions.After the macroscopic and microscopic test of the cable aged in different air pressure environment,it is found that the air pressure condition has little effect on the aging of cable water tree in the early stage of aging,and in the middle stage of aging,with the increase of air pressure,the aging degree of cable water tree also increases.Combining the macroscopic test results with the microscopic test results of the aged cable under different conditions,the prediction model of the internal water tree density of XLPE cable is obtained by using DC conductivity,0.1Hz dielectric loss factor and aging factor,and the non-destructive testing of aged cable under different conditions is realized.