What is the purpose of a transformer oil pit in substations?

A transformer oil pit, also called a containment pit or bund, is built to capture leaked oil and fire water runoff so it does not spread into soil or waterways. It is designed with volume capacity, drainage control, and sometimes oil water separation media to manage spills. The pit supports environmental compliance and reduces cleanup costs after failures, bushing leaks, or tank ruptures. In many designs it also supports fire safety by limiting the spread of burning oil and guiding runoff to a controlled area where suppression systems can be more effective.