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| The Influence of Convective Characteristics of Saturated Porous Media on Ampacity Performance of Submarine Cable |
| Liu Shili1, Luo Yingnan1, Liu Zongye2, Fu Zhuangu1, Liu Qingda3 |
1. Key Laboratory of Modern Power System Simulation and Control & Renewable Energy Technology Ministry of Education Northeast Electric Power University Jilin 132012 China;
2. State Key Laboratory of Advanced Power Transmission Technology Global Energy Interconnection Research Institute Co. Ltd Beijing 102209 China;
3. State Grid Jilin Power Supply Company Jilin 132011 China |
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Abstract In recent years, as countries attach importance to energy decarbonization, offshore wind power, with its advantages of high energy efficiency and being suitable for centralized development, has gradually become one of the key directions of energy transformation. The high-voltage submarine cable is an important part of the offshore wind power transmission system, so it is of great significance to build an accurate multi-field coupling model and accurately analyze the heat transfer process between the submarine cable and the surrounding medium for improving the economy of the offshore wind power system.
The operating environment of submarine cable is quite different from that of land cable, and the most obvious difference is that the heat transfer process between submarine cable and surrounding medium involves not only heat conduction but also more complex convection heat transfer process. However, the current carrying characteristics and temperature field of submarine cables are mainly studied based on the thermal circuit model and finite element method commonly used in the research of terrestrial cables. Most of the literatures ignored the complex convective heat transfer process between porous media and sea water and the influence of permeability parameters on the overall heat transfer process, which led to large errors in the analysis of current carrying performance of submarine cables, affecting the economy of offshore wind power system and the evaluation of transmission capacity of AC submarine cables.
In this paper, considering the characteristics of porous media of seabed sand and the convective heat transfer process between seawater and porous media, a multi-physical field coupling analysis model of electricity, magnetism, heat and flow of submarine cable is established. The sand under cable laying is simulated from a generally simplified compact solid without pores to a porous medium allowing seawater to flow. On this basis, the influence of porous media on the cable heat transfer process under submarine laying conditions is analyzed in detail, and the fluid field, temperature field and convective heat transfer intensity in the porous media around the cable under different permeability are analyzed. The effects of permeability, thermal conductivity, cable burial depth, three-phase spacing and other factors on cable core temperature are studied. The influence of permeability on current carrying performance of submarine cable is discussed by comparing with IEC calculation results.
The following conclusions can be drawn from the simulation analysis: (1) The existing calculation methods ignore or underestimate the convection heat transfer process around the submarine cable, resulting in conservative calculation value of current carrying capacity. (2) The permeability of porous media has a significant impact on the heat transfer process and current carrying characteristics of submarine cables. When the permeability is greater than 10-12 m2, the convection heat transfer process in the media around the cable is dominant, and the current carrying capacity of submarine cables is greatly improved compared with that of terrestrial cables. (3) When the permeability is less than 10-12 m2, the heat conduction process mainly occurs in the medium around the cable. At this time, the temperature field and current carrying capacity of the submarine cable are similar to those of the land cables. Sometimes the current carrying capacity of submarine cables is even lower than the direct buried cable on land. This is because the thermal conductivity of porous sediments such as clay with low permeability is even lower than that of land soil, which makes the cable core temperature higher than its design temperature in the land environment (90 ℃).
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Received: 27 October 2021
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2023, Vol. 38 
