The influence of gravel on the ambient temperature of power substations

This paper examines the role of gravel in the heating process of substation environments. The choice of the material applied to the electric energy substation surface level can influence temperature changes in equipment. Ambient temperature is an important parameter used to define how many years a transformer will last when subjected to a load curve, under normal and emergency operation conditions. This paper shows that the ambient temperature of 30 °C, suggested in IEEE C 57.91 standard for calculating transformer's loading depending on the desired equipment life span is underestimated. There are differences in ambient temperature on surfaces when applying different rocks on the soil surface substations. In terms of the resistivity, some rocks have higher values than others when the drain systems fail to drain all the rainwater to the soil. Two field tests were performed, one in the 345 kV/138 kV Jacarepagua Substation in Rio de Janeiro, and the other in the Substation of Foz do Iguaçu in the state of Paraná, where measurements were performed at three locations: switchyard of 600 kV direct current - DC, 500 kV and 750 kV alternating current - AC. Laboratory tests of thermal and electrical properties of rocks typically used to cover the ground of substations were also performed. This paper presents some consideration of drainage properties.