Heat Transfer Problems of Distribution Transformers in Open Underground Vaults

Abstract

An idealized model for heat transfer problems of an underground distribution transformer, where the unit is placed in an uncovered vault, is studied. The work emphasizes the steady state operation of transformers, in which the time rate of heat generation is constant and the temperature distribution depends only on spat1al coordinates. Such an approach much simplifies the numerical calculations, while providing important inf ormation concerning various factors which affect the temperature distribution. It is shown that Increasing the vault size, in particular the diameter, has the most pronounced effect in reducing the transformer temperature rise. Other factors such as thermal conductivities of vault and surrounding soil, and the emissivities of tank and vault surface, have only minor effect.