How does a transformer oil dryer remove moisture from oil?

A transformer oil dryer removes moisture using vacuum dehydration, heating under controlled conditions, or adsorption media. In vacuum dehydration, oil is sprayed or thin filmed in a vacuum chamber so water boils off at lower temperatures, then vapor is condensed and removed. Some dryers use molecular sieves or desiccant cartridges to adsorb water. Effective drying lowers ppm moisture, improves BDV, and helps shift equilibrium so paper insulation gradually dries over time, reducing long term aging risk.