Cooling of Distribution Transformers in Vented Underground Vaults

The thermal performance of an instrumented distribution transformer in a vault was measured and compared for still air ambients and low-speed wind with various covers (grates and caps) and flow-control barriers and splitters. Correlations for free convection from the tank and vault as well as correlations of the thermal impedances due to air recirculation for various cover and flow-control designs were obtained using the data and thermal network analysis of the radiant and convective transfers. Data show distributions of oil, tank wall and cover temperatures, heat fluxes, and thermal conductances.