Partial Discharge Detection Of Typical Defects For DC Cables Based On Damped AC Voltage

At present,the research on the partial discharge of cross linked polyethylene(XLPE)cable is mainly conducted by DC pressure detection with constant polarity.The partial discharge signal is difficult to be excited and the collected PD information can not be analyzed well.It is of great significance to study the new PD detection method of DC XLPE cable.This paper explores the PD detection of typical defects in DC cable based on damped oscillation voltage,studies the influence of different DC pressurization time,different DC voltage amplitude and different oscillation frequency on PD excitation,and puts forward the recommended PD detection method of DC cable based on damped oscillation voltage.Firstly,the distribution of electric field intensity in the model is calculated by simulation,which is based on the needle tip defect and bubble defect of DC cable,which is the interaction of the external applied electric field,the interaction between the external applied electric field and the space charge,and the heteropolar external applied electric field and the space charge after polarity reversal.Secondly,the experimental platform of the model PD characteristic oscillation wave detection is built to change the DC duration and voltage amplitude of the oscillation wave voltage,and the relationship between DC duration and voltage amplitude and PD excitation is studied.Finally,the capacitance inductance of the experimental circuit is changed,and the relationship between the change of the frequency of the oscillation wave and the characteristics of the partial discharge is studied.The results show that when the external electric field and the space charge electric field act together and the two electric fields have the same direction,the electric field intensity in the model will increase significantly,which is conducive to the excitation of partial discharge;adding a period of DC voltage or increasing the frequency of oscillation wave voltage can detect the partial discharge of DC cable well.With the increase of oscillation frequency,the initial voltage of partial discharge decreases and the amount of partial discharge increases.The above phenomenon is more obvious in the defects of electric field concentration,and the sensitivity of defect detection is relatively high;it is feasible and effective to use damped oscillation voltage to detect the partial discharge of DC cable,and the best detection effect is to extend the DC pressurization time Δt=15min and select the highest oscillation voltage frequency in the range of 20-500Hz.