| With the global emphasis on environmental protection and renewable energy,clean energy generation gets an unprecedented development,one of the important aspects is the offshore wind power.China's wind development 'thirteen five' plan to actively and steadily promote the domestic offshore wind power construction,the development of offshore wind power will also lead to more submarine cable engineering applications,because the grid integration of offshore wind power will rely on submarine cable.At the same time,in order to enhance the reliability of offshore island power supply,China has carried out a number of large-scale submarine power cable transmission projects in recent years,such as Hainan 500 kV AC submarine cable grid integration project,Zhejiang Zhoushan,Fujian Xiamen and Guangdong Shantou HVDC transmission technology projects etc.In these cross-sea power transmission projects,submarine power cables work as the main device connecting at both ends of substations or multi-terminal converter stations,played an extremely important role.Submarine power cable has complex structure,extremely high production process requirements and comprehensive electrical and mechanical performance requirements.And its operating environment is much worse than the terrestrial cable,inconvenient for monitoring and maintenance.Besides,there are no specifications or standards for submarine cable ampacity calculations worldwide.In order to ensure the safe and reliable operation of the submarine power cable,it is necessary to carry out submarine power cable ampacity analysis and calculation.The purpose of this thesis is to analyze and calculate the temperature field distribution and submarine cable ampacity under different flexible and rigid joint connections.Power cable flexible and rigid joint-respectively,refers to the connector at the cable conductor connection using welding and crimp connection.Most of the existing power cable ampacity calculation is based on IEC-60287 standard using thermal analysis or temperature field numerical calculation.Most of the temperature field is calculated on the cable body cable core,without considering the impact of cable joints.And due to poor production process or production operation is not standardized of cable intermediate joint,joint conductor's contact resistance can be unusually high which cause uneven heating to the insulation will lead harm to the power cable.In this thesis,the structure model of flexible and rigid joints of submarine power cable is constructed,and the mathematical coupling model of the electromagnetic field and temperature field of the submarine power cable joint is established.The finite element method is used to analyze the temperature distribution of the submarine power cable joints and the calculation of the ampacity of the submarine cable.It is of great practical significance to make the load plan of the cable operation department and ensure the safe and reliable operation of the submarine power cable.The main research contents of this thesis include:(1)The different laying methods of submarine cables are analyzed.And based on the theory of cable electromagnetic field and the basic law and equation of temperature field and heat transfer,the mathematical model,control equation and boundary condition of electromagnetic-thermal coupling field are studied.The coupling mechanism and solving steps of the interaction between the electromagnetic field and the temperature field during the operation of the submarine cable are analyzed.The validity of the model is verified by comparing the theoretical and experimental results with the simulation results.(2)The COMSOL-Multiphysics software was used to establish the 3-Dimensional electromagnetic-thermal coupling model of the flexible joint and rigid joint of the 110 kV submarine cable,respectively.The temperature field analysis and calculation of two joints are also carried out respectively.Based on these models,the influence of load current on the temperature characteristics of submarine cable joints are studied.And the influence of the contact resistance of crimp connector on the temperature field of the cable rigid joint is analyzed.All these work will contribute to the approving of the submarine cable ampacity.(3)Calculated the temperature field and ampacity of 110 kV AC submarine cable,which was laying in 3 methods-underwater soil buried laying,laying in seawater and laying in the pipeline in landing section of the cable.The effects of embedding depth,soil thermal resistivity and seawater temperature on the ampacity of the submarine cable were analyzed,respectively.Finally,Calculated the temperature field and ampacity of±500kV DC submarine cable in soil buried laying and compact laying method,verificated the ampacity enhancement of external forced cooling. |
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