The standard has undergone revisions, with the most current version being (reaffirmed in 2019). Older versions (e.g., IEEE 980-1994) are often cited in legacy designs, but modern engineers require the latest PDF to incorporate updated soil resistivity measurement techniques and fault current modeling.
Modern substations rely on oil-filled equipment: transformers, circuit breakers, load tap changers, and regulators. A single large power transformer can contain over 20,000 gallons of mineral oil. In the event of a catastrophic tank rupture, leak, or maintenance error, that oil becomes a hazardous substance. ieee 980 pdf
