Thermal Modelling of High Voltage Electrical Network Cables for Maximisation of Transmission Capacity in Underground Network Systems

Underground cables are an essential part of the modern electricity grid, especially in urban areas and offshore settings where overhead cables can be undesirable or impractical. With the continued increase in the electrification of end use, there is a heightened focus on maximising the transmission capacity of existing and new underground cable infrastructure. This research aims to assist grid operators in maximising the dynamic transmission capacity of underground circuits by investigating the factors that influence the ampacity ratings of cables. The thermal behaviour of 110 kV XLPE-insulated cables, laid in trefoil formations in single and triple-circuit trenches, was analysed by means of a validated computational fluid dynamics model. Compared to industry standard software, the current investigations indicate that it may be possible to increase the ampacity of single-circuit cables by up to 4.8% in winter conditions and 9% in summer conditions. Likewise, for triple-circuit trefoil arrangements, ampacity enhancement possibilities of 9.3% were observed. Equal loading of cables was found to be most efficient loading combination resulting in the highest overall capacity of independent triple-circuits running parallel in the network.