Study On Signal Characteristics And On-Site Measurement Of Partial Discharge In XLPE Power Cable

Cross-linked polyethylene(XLPE) cable has been widely used in urban distribution system thanks to its excellent physical, chemical and thermal duration properties. Due to the presence of impurity, cavity in XLPE insulation, partial discharge can be initiated that finally gives rise to the breakdown of the insulation. This may have a catastrophic influence on the safe operation of power system. From the viewpoint of safety, partial discharge detection and insulation diagnosis of XLPE power cable is essentially important.In this paper, a high frequency current transformer(HFCT) was employed with a bandwidth from 100 k Hz to 30 MHz to capture the partial discharge signal introduced within three typical defect models, i.e. internal discharge, corona discharge and surface discharge. The single discharge pulse as well as the discharge sequence were obtained by the HFCT and were analyzed with the purpose of feature extraction.As regards to single discharge, the frequency spectrum shows dependence of magnitude distribution upon the defect models. Furthermore, the effect of defect size of models(including the diameter of the cavity, the length of the needle electrode, the diameter of the needle electrode and the interval between the needle tip and the XLPE sample surface) on the single discharge pulse shape was investigated. It was found that the rise time, pulse width and the magnitude was strongly dependent upon the defect size and was varied as a function of the model type.Discharge sequence was also analyzed by means of N-Q distribution. A twoparameter Weibull Distribution method was employed to characterize the N-Q distribution, and the two parameters ? and ? were calculated by Least Square Method. It was found that the parameters ? and ? for different defect models exhibit obvious cluster features that can be used to identify the discharge model.On-site partial discharge measurement was performed with XLPE cable terminals which were about to operate in a 35 kV substation of a company in Tianjin. By analyzing the PRPD and signal pulse characteristics, the defect type that may be within the cable terminals were speculated.