Structure Characteristics Analysis And Optimization Design Of 110 KV High-voltage XLPE Cable Shield Layer

At present,the application of XLPE cable in urban power transmission and distribution system is more and more extensive.At the same time,the service life and performance of cable are widely concerned.The electrical and thermal characteristics of XLPE cable are important factors affecting the performance of cable.As an important part of cable structure,the metal sheath and waterstop of cable have obvious differences with the adjacent insulation layer and sheath.However,the current research lacks the in-depth study on the electrical and thermal characteristics of metal sheath and waterstop.Through the special analysis and Research on the electrical and thermal characteristics of the high voltage XLPE cable sheath structure,it can provide a solid theoretical basis for improving the calculation accuracy of the current carrying capacity of the cable and the operation life of the cable.In this paper,the relative permittivity,thermal conductivity,coefficient of thermal expansion and modulus of elasticity of XLPE main insulation material and sheath structure material are measured at different temperatures.The electrical,thermal and mechanical parameters of 110kV cable insulation and sheath material and the law of change with temperature are obtained.According to the structural characteristics of 110kV High Voltage XLPE cable,the physical model of radial and axial structure of the cable is established,and the electric field distribution,temperature distribution and thermal stress distribution characteristics of the cable are calculated by AN SYS finite element analysis software.The calculation results of the electric field distribution show that the electric field strength of each layer of XLPE cable in normal operation will not be higher than the breakdown field strength of the dielectric without considering the circulation of the metal sheath;however,when there is a gap between the water stop band and the metal sheath,the electric field strength in the air gap will be greater than the breakdown field strength of the air,and the air gap breakdown will occur.The calculation results of temperature distribution and thermal stress distribution show that the overall thermal conductivity of the cable can be affected by changing the structural parameters of the cable sheath,such as the rolling pitch,the rolling depth and the thickness of the waterstop.Based on the calculation results,the optimization scheme of the sheath structure is proposed,which is to shorten the crimp pitch of the corrugated aluminum sheath of the cable to the original size range of 2/3 and 1/2,reduce the crimp depth of the aluminum sheath and the thickness of the waterstop,at the same time,the thickness of the aluminum sheath,the thickness of the air gap and other structural dimensions of the XLPE cable remain the same,and then verify the calculation and compare with the original structure.It is found that the temperature difference and thermal stress of the sheath structure are smaller than that of the original sheath structure,and have better electrical and thermal characteristics.