A mobile transformer oil treatment plant is used when oil purification must be performed on site without draining or transporting oil off location. Typical scenarios include substation maintenance, emergency moisture ingress, oil aging detected through testing, or post fault recovery. These units perform vacuum dehydration, degassing, and fine filtration while the transformer remains energized or de-energized, depending on procedure. Mobile plants reduce outage time, lower logistics costs, and minimize contamination risks. They are especially useful for large power transformers where oil volume is high and transport is impractical.