Analysis Of Ampacity And Insulation Eletric Field Of AC XLPE Cable Line Transformed Into DC Operation

Line Retrofitting can fully utilize the existing transmission corridor,sharply improving the transmission capacity of the line.With the development of flexible high voltage direct current(HVDC)technology,the transformation of the AC cable line into DC operation has been paid more and more attention.Therefore,the accurate calculation of the DC ampacity and insulation electric field is of great significance to the safe operation of the AC cable after transformed into DC transmission mode.In this paper,the YJLW03-48/66kV-400 type single core AC cable is taken as the research object,and the ampacity and insulation electric field are analyzed.First of all,the thermal characteristics of the cable are analyzed from the view point of heat transfer,and the DC ampacity of AC crosslinked polyethylene(XLPE)cable laid in the air is analyzed by analytical method,numerical method and experimental method.Then,using analytical method to calculate AC ampacity of the three-phase AC cable directly buried installation,combined with the actual capacity expansion project,and based on the actual capacity expansion project,the ampacity of AC cable directly buried installation transforming to bipolar DC operation is determined.Finally,the conductivity mathematical features of AC cable material under DC voltage was analyzed,establishing the mathematical model of conductivity-(temperature、electric field).With the help of COMSOL multi-physics software,the insulation electric field is analyzed when the AC cable is changed to DC operation.and studied electric field distribution by means of the multi physical field coupling analysis software.At the same time,the model test is carried out to perform a full verification of the cable,and the effect of the cable line to the DC operation is evaluated.The DC ampacity of AC XLPE cable laid in the air was determined through the experiment,which verify the accuracy of the analytical method in the calculation of ampacity of high voltage(66 kV)cables.The DC ampacity(710 A)of AC cable directly buried installation.When the load is 100%,the electric field of the insulation layer is reversed.AC cable is verified by electrical type test,and calculating the capacity multiple.The research results can provide support for the rehabilitation of the northeast city power grid 66 kV cable lines,but also lay the groundwork for the transformation of the AC cable line into DC operation in the future.