Thermal Analysis of Submarine Cable Routes: LSM or FEM?

For environmental reasons stringent legal constraints have to be considered for the design of submarine cable routes for offshore-windparks in the North Sea and the Baltic Sea. Although the line source model (LSM) for thermal analysis is approved in general, there is still a controversial discussion whether the calculation methods basing on LSM are sufficient, or if the finite-element-method (FEM) should be applied. In this paper, a concrete problem -a submarine cable of the type FXBTV, 3times800 mm², 150 kV from ABB, laying in the Wadden Sea- is analysed by both methods. Ideal heat sinks as well as heat transfer by convection are investigated and also the influence of varying seasonal soil temperatures is considered. For the examined problem the temperature of the seabed is mainly defined by the seasonal temperature curve. Variations in the power loss of the submarine cable causes only negligible temperature fluctuations with respect to the seasonal indicated temperature fluctuations. It will be shown that both methods are suitable to compute highly reliable results for the test point´s temperature in the far field, LSM causes much less computation effort than FEM, but FEM also shows reliable results for the near-field (e.g. core temperatures of the cables) and it is suitable to compute more complicated problems.