Research On Calculation And Improvement Methods For Ampacity Of Cable Installed In Short-conduit

Power cable plays an important role in urban transmission and distribution network.Accurate thermal rating of cable lines is conductive to fully utilizing the present infrastructure and optimizing the future investments.A short-conduit is commonly used to provide mechanical protection for the cable in urban underground environment,and it is also a common thermal bottleneck for the lines.However,the thermal rating for the cable in the short-conduit is not specialized in the IEC 60287.And there is a lack of the method for the real-time thermal rating of the short-conduit cables.Moreover,the effects of different filling materials to improve the ampacity of cable installed in short-conduit is not clear.Based on this background,this paper has conducted the research on the calculation and improvement methods for ampacity of cables installed in short-conduit.In this study,the existing amapcity assessment methods for the cable installed in shortconduits are firstly investigated.An example calculation is carried out using these methods and the shortcomings of them are analyzed.Secondly,combined with COMSOL Multiphysics,a three-dimensional thermal-fluid coupling field simulation model of the cable installed in shortconduits is established,and the calculation results were compared with IEC 60287 to verify the accuracy of the model.Based on the verified model,the axial conductor temperature distribution of the cables with dfiferent condictions are calculated.The effects of axial heat transfer on the conductor and the ampacity of the cable installed in short-conduits are investigated.The characteristics of surface temperature distributions are also analyzed,which provides a foundation for the improvd method.Then,the improved quasi-three-dimensional thermal model of cable installed in short-conduit considering axial heat transfer was established,and the simplified method and iterative solution method of the model were proposed.The calculation results were compared with the finite element simulation and IEC standard,which verifies the effectiveness and safety of the improved model.Finally,the improvement of different filling materials on the steady-state and short-term current carrying capacity of the cable installed in short-conduits were calculated and compared.Based on finite element simulation and heat transfer theory,a three-dimensional thermalfluid coupling field simulation model and an improved quasi-three-dimensional thermal model of the cable installed in short-conduit are established in this paper,which can be used to realize the real-time assessment of the cable installed in short-conduit of’ ampacity and to analyze the influencing factors of it.The improvement of different filling materials on the ampacity of cable installed in short-conduit is compared,which can provide a theoretical basis for the improvement such cable lines.The reaserch work done by this paper can provide support for the power department to excavate the potential transmission capacity of such lines.