Thermal simulation for distribution transformers in underground vaults

This paper presents the thermal simulation of the load behavior of a transformer in an underground vault so as to establish maximum loading without loss of life. In that way it optimizes the utilization factor of the transformers in underground distribution systems. The simulation carried out by a set of differential equations relating heat flow from the transformer to the vault and the forced extraction of air from the vault to the environment. The software supports different daily loads and ambient temperature cycles, vault configurations and amounts of air extraction, forced or natural. The results of the simulations were matched with field measurements in existing vaults and the results obtained were extremely positive, thus the program optimizes the utilization factor of transformers in underground vaults.