What is the difference between filtration and purification of wind turbine transformer oil?

Filtration and purification are both processes for improving the quality of wind turbine transformer oil, but they target different impurities. Filtration primarily removes solid contaminants like dirt, metal particles, and sludge using filters, while purification goes beyond filtration by addressing dissolved gases, moisture, and chemical impurities. Purification often involves degassing, dehydration, and sometimes regeneration of the oil through chemical treatments to restore its dielectric properties, making it more comprehensive than filtration alone.