Study On The Space Charge Characteristics Of XLPE Cable Based On Temperature Gradient Field

With the rapid development of urbanization,that overhead line is replaced by cable become a must.with the excellent Electrical Performance,XLPE cable is widely applied in the construction of urban electric power network.Study the aging mechanism of XLPE cable insulation is a significant thing,it is of important significance on the cable failure prediction and the power system reliability.As we know,Space charge ranks the top position among the aging breakdown theory of polymer insulation.Space charge causes the distortion of electric field and the failure of microstructure,and in turn it accumulates more space charge.That creates a vicious circle until insulation breakdown.In the actual operation of cable,there is a temperature difference between insulation's interior and exterior because of the heating from cable core.The temperature difference affects electric field distribution and then the aging.As a result,in this paper,in order to find out the law of space charge characteristics development with aging under temperature gradient field,complete the aging properties of cable's insulation,we have an Electro-thermal combined aging on lOkV cable under temperature gradient field and study Space charge characteristics from several angles.This paper has an Electro-thermal combined aging on 10kV cable which has run 15years under temperature gradient field.The voltage is 34.8kV and temperature gradient field is 115 ? and 80 ?,the aging time is 200days and it is divided into 5 stages.We measure on-line the space charge distribution of cable regularly and observe the gather and migration.And after the end of each stage,slice cable into section samples and have the space charge experiments on the samples including AC and DC.In order to corresponding to the result of space charge measurement,test measurements include power frequency breakdown X-ray diffraction(XRD),frequency domain dielectric spectroscopy and gel content are experiment on slices.Experimental results show that:(1)In ageing process,the space charge of cable accumulate and then transfer,the movement is a out-migration from the inner,charge density decreases constantly and the speed decreases constantly.Contrast with another experiment,we find that the voltage is more high,and the speed of charge transfer is more fast,the time of charge move is less.(2)The charge accumulations of cable slices under DC or AC are different,because it is not same that traps of insulation respond under stimulations of different electric field.But there is also commonality between DC and AC:quantity of electric charge have an overall rise with aging,compared quantity of electric charges among three parts of cable,the inner is largest,the middle is followed and the outer is smallest;In the process of depolarization,decay time constant have an overall decrease.(3)There is a well corresponded relationship between changing curve of breakdown field strength and the AC quantity of electric charge,that mean space charge is of importance to breakdown field strength;The results of the gel content experiment,XRD and the frequency domain dielectric spectroscopy is different with the result of power frequency breakdown experiment,that means physicochemical properties have less impact on aging.