Research On Power Cable Insulation Detection Based On Partial Discharge Envelope

In recent years,with the development of power industry,the power cable attracts attention of the power sector because of its superior power transmission capacity.Its operation reliability is related to the normal operation of power system,so it is very important to detect the fault of power cable.Power cable’s fault is closely related to its insulation state,the major insulation’s defects will inevitably lead to partial discharge(PD)phenomenon.Therefore,PD detection of the power cable is the most direct and effective method of cable insulation evaluation.This paper takes XLPE power cable as the object of study.Firstly,it is introduced the current research status of cable insulation detection technology at home and abroad,and the commonly used detection methods of PD.On this basis,it is analyzed the mechanism of partial discharge and the anti-interference scheme.Secondly,the propagation characteristics of PD signals is studied:choose the double exponential function model as a reference for the PD signal mathematical model and study mathematical relationship of the waveform and parameters;establish the cable’s distribution parameter equivalent model and study propagation law of PD signal theoretically;it is established the PD signal simulation model and cable simulation model and simulation circuit is also built by using SIMULINK components in MATLAB.Through the simulation of transmission characteristics of the PD signal in the cable,it is provided a theoretical guidance for the actual testing of cable insulation.Then,the paper put forward the PD signal acquisition device based on the electromagnetic coupling method.According to PD detection’s requirements,it is selected the high frequency current sensor based on Rogowski coil.The detection frequency range is given and the appropriate sensor parameters are selected.After the performance test,the signal sensor has the characteristics of high sensitivity,wide detection frequency band and good frequency characteristics,and meets the actual requirements of XLPE cable PD detection.A preamplifier circuit associated with a sensor is designed to amplify the PD signal.Finally,according to the problem of the XLPE cable insulation which is prone to be defective and the partial discharge signal is susceptible to interference,this paper is proposed a method to diagnose and evaluate the insulation condition of the cable by means of the envelope of the partial discharge signal.The principle of this method is to calculate PD signal envelope on both ends of the cable by Hilbert transform,andGauss pulse is used to model the envelope,and the time variable(pulse width,slope and down slope and phase)of envelope correlation is used to distinguish PD type.In order to compensate the influence of PD propagation’s dispersion,it is proposed dispersion compensation to change the width of the envelope.Then the location of the discharge is calculated according to the arrival time difference of the envelope.The experimental results show that the proposed method improves the positioning accuracy.