On-line Partial Discharge Monitoring And Assessment System Research Of XLPE High-voltage Cable Joint Insulation

Because of the rapid development of the electrical power industry, an increasingamount of cross-linked polyethylene cables have been used. Therefore, more and moreattention has been paid on XLPE cable insulation condition, especially on XLPE cable jointinsulation condition, because most of the problems for XLPE-insulated cable systems arecaused by internal defects of the joints which have to be mounted on-site. In this paper, theon-line monitoring for partial discharge, the technology of interference suppression for thecable joint as well as the assessment of insulation condition are studied based on theMulti-layer composite insulate properties of the cable jointIn order to estimate the insulation condition of the cable, Researches aboutelectromagnetic parameters such as the structures, the materials cable joint were conductedand a comprehensive analysis of various on-line monitoring methods was done, after whicha novel on-line partial discharge monitoring method based on the principle ofhigh-frequency electromagnetic coupling and differencing for the insulation of the cablejoint was proposed from the point of view of practical application. The rogowski coil,conditioning circuits and transmission networks in the new on-line partial dischargemonitoring system for the cable joint were also considered. In addition, the characteristicsof the rogowski coil, conditioning circuits in the online monitoring system were simulatedin order to prove the validity this system.Meanwhile， the partial discharge signal is relatively weak, and is easily drowned bythe noise on line, thus, not only a high signal-to-noise ratio of signals sampled by the sensorhardware circuit in the system but also the software technology of interference suppressionto sample valid signals from the noise on line is considered in this system. Because periodicinterference, white noise and pulse interference are widespread in the partial dischargesignal, and multirate filter based on wavelet theory is used to suppress the noise to get thetime-domain waveform of the partial discharge which can be easily separated from noisesignals for the convenience of extraction, and is proved by the simulation software.Moreover, with the above theory and simulation, this paper based on the weight proposes anew assessment criteria for the insulation of XLPE cable joint,and a theoretical study onthe impact factor in this assessment criteria，to provide a reference for the technicalmeasures.