Investigation of the Electromagnetic Fields of a HTS-Three Core Cable Arrangement at Mains Frequency for the Determination of Electrical Properties by Using FEM

Abstract

The increasing requirements on the sensitive infrastructure of transmission and distribution grids due to renewable energy sources and increasing electrification necessitate continuous optimization, new constructions and reinforcement efforts. In addition to conventional high voltage transmission systems, superconducting underground cables represent an attractive alternative to overhead power lines and conventional underground high voltage cables especially in urban environment where space is an issue. Superconducting cables are characterized by low transmission losses, higher transmission capacity and low space requirements due to the absence of heat input into the ground. In addition, new constructions become possible due to the specific capabilities of superconducting materials. Thus, comparatively low emission of magnetic flux density is observed. This is especially applicable for urban areas and bottlenecks, since the compact design of the high-temperature superconductor cables (HTS cables) and the reduced space requirement leads to a significant reduction in the civil engineering expenditure and to a reduction in installation costs. As an example, it is possible to achieve a transmission power of 400 MVA with a single 3-phase 110 kV three-core cable instead of up to five conventional 110 kV single-core standard cable systems. The costs for road surface and civil engineering can be reduced by up to 80%, which is especially advantageous in cities with high traffic volumes or historical buildings and grounds. This leads to a larger acceptance by the population. At the same time, the technology offers the possibility of transmitting higher powers at lower voltage levels (e.g. 110 kV level instead of 400 kV level), resulting in further significant cost reduction due to the elimination of transformers and switchgears at the higher voltage level, and also saves precious space in inner-city areas where ground space is very expensive. This paper reports about previous investigations, which have shown that a 110 kV three-core cable satisfies the requirement of a compacted structure more satisfactorily than a triaxial system. Further investigations will validate the results of the superconducting three-core cable by a sensitivity analysis. The influence of different outer conductive layer materials on the magnetic fields is investigated and evaluated. The inductive and capacitive cable properties of the superconducting arrangement are determined and compared with conventional energy transmission systems in order to estimate the behavior in the transmission network. The investigations serve to verify the feasibility of the construction of a HTS cable connection in the inner city area of the city of Munich. The cable is supposed to enable the installation in an existing, former GAD steel tube and reduce the high costs for civil engineering and road construction to a minimum.