Abstract
Power cable grids play an important role in the distribution of electric power. The current carrying capacity (ampacity) of cables is primarily limited by the thermal limit of the cable. Current standards for ampacity calculations are given in IEC 60287 and IEC 60853 and are based on derivation of analytical expressions with many simplifying assumptions and empirical expressions special cases. This causes a lack of flexibility and resulting calculated ampacity can in many cases be conservative. Using finite-element analysis (FEA) modelling of electro-thermal problems overcomes the lack of flexibility and potentially conservative results and is an emerging solution for doing ampacity calculations. Several reference cases relevant for distribution grids, as presented in CIGRE Technical Brochure 880, is implemented in a FEA-based software tool developed for Norwegian and international utilities. It is shown that the calculated ampacity generally is in good agreement with the IEC standard. Novel ampacity tools, such as the work presented here, provides new possibilities for utilization of the power cable grid. E.g., the ampacity can be re-calculated for existing cable installations, surveying possibilities for increased utilization or in the opposite case down-grading the ampacity to ensure security-of-supply.