Simulation Research On Electric Field Of AC/DC Cable Joints

Now all the cable line in the city are based on the AC power supply,so its reliability directly impacts on the operation safety of the public facilities and people's life,and the electric field simulation is one of the most important methods of electric power equipment failure analysis.Compared with the AC power cable,the DC power cable has advantage of the bigger transmission capacity,the smaller energy loss and the narrower transmission line corridor,so now DC power cable becomes a hot issue.In order to reduce costs,some scholars propose that we can make the AC power cable to operation on the DC electric field.But taking into account the high costs of the experiment,we should research this issue by simulation method at first.From the above reasons,researching the simulation method on AC and DC electric field is significant.At first,this paper introduces electrostatic field,quasi-static electric field and stable current field,and meanwhile combining the theory of dielectric polarization,some conclusions are drawn: On AC electric field the selection of electrostatic field or quasi-static electric field are based on material conductivity;On DC electric field we should analysis the electric field distribution by stable current field.Secondly,the paper takes 10 kV AC XLPE power cable and joint as the study objects.We compare the electric field distribution of the power cable insulation on electrostatic field and quasi-static electric field,and get that because the volume of semiconducting materials in 10 kV AC XLPE cable is very small,we can select the electrostatic field as the method to analysis its electric field distribution.Then we discuss the simulation method of 10 kV AC XLPE power cable joint,and get that we should use the quasi-static electric field to analysis its electric field.Meanwhile,we find that for the intact joint or the joint which have the defect that don't destroy the axis symmetry of the cable joint,their field simulation could be based on a two-dimensional axisymmetric model.But for the cable joint which have the defect that destroy its axis symmetry we should take the three-dimensional model.We also discuss the relationship between breakdown voltage?partial discharge inception voltage and electric field distortion of some cable joints with typical defect,and combining the experiment data we further verify the accuracy of the quasi-static electric field.At last,we take the Shanghai Nanhui 30 kV DC XLPE power cable which has the space charge data report and has the 4mm insulation layer to simulate the DC power cable electric field distribution.We take the layered model to calculate the current electric field on limit power,rated power and polarity reversal,and combing the space charge data we calculate XLPE power cable insulation layer electric field on 30 kV DC voltage.Then we measure the conductivity of SIR and EPDM on different temperature and electric field,and combing the data with the Maxwell-Wagner theory we think we should select the ERP as the insulation material of DV cable joint.Meanwhile we simulate the distribution of current electric field in DC cable joint on the condition that the accumulation of interfacial space charge is the least.Combing the simulation result with actual situation we think making the AC power cable to operation on the DC electric field has some feasibility.