Thermal behaviour of medium-voltage underground cables under high-load operating conditions

•Numerical, experimental and simulated model of MV underground cables is presented.•A comparison of the IEC standard and UNE standard (simplified IEC) is performed.•The simplified standard is less accurate than the IEC (with dry zone formation).•UNE 211435 has a minor error when depth is less than or equal to 0.6 m. The dynamic management of electric power distribution lines has become a topic of great interest at present. Knowledge of the ampacity of cables is fundamental to carrying out dynamic management. In this study, the ampacity of buried cables in different soil resistivities and depths was calculated. A small-scale model was built in the laboratory to simulate the operating conditions of a buried cable. With the experimental results, a numerical model based on the finite element method was validated to evaluate the ampacities calculated by two standards. A comparison was made between the ampacities calculated from the IEC 60287-1 and UNE 211435 standards and those obtained from the simulated model. In addition, a comparison was made regarding the steady-state temperatures obtained at each calculated ampacity. The results obtained from the simulated model design show that the ampacity calculation method of the IEC 60287-1 standard where drying-out of the soil occurs is the most accurate, and has the least risk of exceeding the maximum permissible cable temperature.