| The development of islands in the South China Sea has an important strategic position for our country.At the same time,the effective use of marine renewable energy also has great economic and environmental value.Submarine cables have undertaken important power transmission tasks in this process.The ampacity of submarine cable is related to the safe,stable,and economic operation of the power transmission system.How to calculate ampacity of submarine cable scientifically and accurately,and at the same time solve the problem of the reduction of ampacity of submarine cable due to the deterioration of the heat dissipation environment after landing on the shore,which troubles the power operation department difficulty.The advantages of HVDC cables in terms of transmission distance,capacity,and loss are prominent,and with the development of flexible DC transmission technology,the number of cross-sea HVDC transmission projects put into operation in recent years has increased significantly.At present,there is no standard to calculate the ampacity of HVDC submarine cable.The IEC standard to calculate the ampacity of land cable is used in engineering.However,the standard does not consider the temperature difference of insulation layer of HVDC cable and the special operating environment of submarine cable,and the result is not accurate enough.In addition,the study on how to effectively improve the ampacity of HVDC submarine cable in the land section is relatively less.In this paper,considering the different laying methods and related influencing factors of HVDC submarine cable in sea area and land area,the calculation method of ampacity is studied respectively,and the ampacity improvement scheme of direct water-cooling cycle is proposed for land area,which provides theoretical support for the determination of technical parameters of HVDC submarine cable in engineering application.The main contents of this paper are as follows:(1)The analytical formula of ampacity of HVDC cable is improved on the basis of IEC standard;The electromagnetic thermal coupling model of HVDC cable body is established,and the iterative calculation method of DC cable ampacity considering the temperature limit of core wire and the temperature difference limit of insulation layer is proposed,which lays the foundation for the improvement of the calculation model of temperature field of HVDC submarine cable in the specific laying environment in the last three chapters,and is compared with the analytical calculation formula through calculation examples.(2)This paper studies the heat dissipation and multi field coupling mechanism of the submarine cable in the sea area.Considering the permeability of the seabed sediment,a multi field coupling model including the body of the HVDC submarine cable,the seabed sediment and the sea water is established.Then,the numerical iteration method is used to calculate the ampacity of the HVDC submarine cable in the sea area,which is compared with the analytical method and the traditional numerical method.(3)Considering the influence of air flow and radiation of HVDC submarine cable in land laying environment,based on the electromagnetic thermal coupling model,the calculation models of cable temperature field for buried,protective pipe and cable trench laying are established respectively;the typical laying parameters of submarine cable in land section are calculated and compared with the analytical method,and the influence of ampacity is analyzed.(4)Based on the three-dimensional thermal circuit model,the micro element iteration method is proposed to calculate the cable ampacity under the direct water-cooling cycle mode.The accuracy of the proposed method is verified by comparing with the field experiment of water-cooling cycle,and the influence of different water-cooling system parameters on the ampacity improvement is analyzed by using the proposed method. |
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