Purification systems typically operate by:

Heating: Oil is heated to reduce viscosity, enhancing purification efficiency.
Vacuum Dehydration: Removes moisture and dissolved gases under reduced pressure.
Filtration: Multi-stage filters capture particles of varying sizes.
Degassing: Eliminates air and gases that reduce dielectric strength.
Adsorption: Uses materials like activated alumina to remove acids and polar contaminants.
The purified oil is then returned to the cable system, restoring its insulating and cooling properties.