Developing simplified thermal models for 11 kV underground cables in Australia

Underground cables are an essential part of the urban electricity grid. However, a disadvantage is that once they reach or even exceed their rated capacity the excessive temperature can considerably shorten the life of their insulation. The ultimate temperature reached is dependent on both the ground temperature and the thermal resistivity of surrounding soil. Modelling the temperature of the core conductor of a cable is highly beneficial because a utility can use this information during emergency overloads to assure that temperature limits are not exceeded, i.e. they can calculate the steady state temperature which would be reached during the overload. The current IEC thermal model requires numerous inputs, all of which might not be available. Consequently, a simpler thermal model based on identifying the transfer function was investigated using data supplied by a utility. The results are presented in this article.