On-line Detection And Location Of Partial Discharge In Medium Voltage XLPE Cable

With the renovation of urban and rural power grid moving forward constantly and the rapid development of the electric power industry,XLPE cables have been widely used for the superior mechanical and electrical properties.The probability of insulation failure of the cable,which will cause a short circuit and even breakdown the system,increases with the accumulation of working hours in the process.Therefore,it is of great significance to carry out the study on the on-line detection of cable insulation for the safe and stable operation of the power system.In this paper,the on-line detection and location of the cable partial discharge was studied,and on the base of traveling wave method two kinds of time delay estimation algorithms were proposed.In this paper,the propagation law of partial discharge signals on XLPE cables was studied firstly,and a cable model was established based on PSCAD/EMTDC,then the propagation characteristics of PD signals in cables was simulated.The simulation results coincide with the theoretical analysis,which verifies the rationality and validity of the cable model,and lays the foundation for subsequent cable PD location and location simulation.The application of AIC information criterion in picking up the initial pulse time was studied,then the two step time delay estimation method based on the time window ener gy ratio and the AIC information criterion was proposed for the defects that can not be p icked up on line.This method was applied to the online positioning,and a multi sensor t raveling wave positioning method was proposed for the uncertain wave velocity in the t raveling wave location process.Firstly,the time window was used to detect the time win dow of the partial discharge,then the local AIC characteristic curve of the time window was obtained,and the initial arrival time of the partial discharge pulse signal was picked up accurately based on the AIC criterion.Finally,the results of time delay estimation ar e applied to the multi sensor online location.The simulation results show that the algorit hm has a high positioning precision,and the relative error is about 0.15% in the noise en vironment with a SNR of-2dB,and it has practical engineering value.In view of the effect of noise on pickup precision,the application of time varying kurtosis in pick-up of pulse initial to moment was studied,and a wavelet packet Kurtosis Algorithm was proposed.Firstly,the time window energy ratio was used to detect the local discharge events,then the main frequency band of the partial discharge pulse was separated in the definite partial discharge window by the wavelet packet,and the maximum time peak value was obtained in this band,which realized the high precision pickup for the initial arrival time of partial discharge pulse.Finally,the simulation results show that the algorithm decreases with the reduction of signal to noise ratio to some extent,but its anti noise ability is strong.Under the noise environment of-14 dB,the location error is less than 2m,which can not only meet the accuracy requirement of high-voltage grid for partial discharge fault online location,but also effectively improve the reliability of power supply.