Research On A New On-line Monitoring Method Of Electric Power Cable Water Tree

With the fast development of the power industry, crosslinked polyethylene cables are widely used in power system. In recent years, the insulation fault of crosslinked polyethylene cables occurs frequently, and the safety and stability of the grid is seriously threatened. Therefore, further study for insulation degradation mechanism of crosslinked polyethylene cables, and on-line monitoring crosslinked polyethylene cable insulation state is of great significance to intelligent power grid construction.On the basis of domestic and foreign study, the aging mechanism of crosslinked polyethylene cable insulation, the formation process of water tree and the influence on cable insulating properties duing to degradation of water tree are studied elaborativly. The existing on-line detection methods of cable water tree also are discussed and compared.Based on the nonlinear characteristics of water tree, the power cable water tree Matlab simulation model is established,using the model for crosslinked polyethylene cable water tree,communication stack assay simulations were performed. The results show that if 50V ac voltage (frequency for 101Hz)is plused on the cable shielding layer,1 Hz tiny feature current can be detected,and the characteristic current increases with water tree deterioration getting futher. Simulation results accord with experimental results,which shows the feasibility of detecting water tree.Because it is diffcult to detect faint feature current, and on-line detection system has low sensitivity, this paper puts forward that chaotic control theory is applied in water tree cross-linked polyethylene cable testing. Duffing chaotic oscillator is sensitive to signal which has the same frequency with periodic signals, and has noise immunity characteristics, so design specific chaotic systems structure. Taking measuring signal as disturbance of duffing chaotic oscillator cycle motive power, achieving accurate measure for 1Hz feature signal,so tiny water tree defects can be found accurately by monitoring system, results of experiments and simulation show the correctness of this method. It is of guiding significance for insulation monitoring of crosslinked polyethylene cable.