Diagnostic Method For Tree-Degradated XLPE Cables

XLPE cable has been experiencing a rapidly growth in renovation project of urban power system. Many electric appliances are connected by cables, whose reliability plays an important role in operation security of the whole power system. The insulation layer of cables would degrade due to the effects of electricity, thermal, mechanical factors and water, thus the operation security and lifespan might be affected. Many researches indicate that tree-degradation (including electrical tree and water tree) is primary cause of cable insulation degradation. Conducting research into the cause of tree-degradation, influencing factors and diagnosis methods has consequential theory and application value in estimation of cable lifespan and maintenance of power supply reliability.The tree-degradation of XLPE cable includes water tree degradation and electrical tree degradation. This dissertation states the characteristics of structure, influencing factors and measuring methods of water-tree, and then makes an analysis of accumulative shape and dynamic properties of space charges in water tree. Water tree may change into electrical tree under the condition of over voltage such as lightening stroke, thereby resulting in breakdown of cable insulation. Conclusions are made on diagnosis methods of tree-degradation and water tree degradation model is constructed, after which simulation of water tree growing process is carried out. Finally, the mechanism and method in locating water tree are reviewed.