How is the oil produced? The journey from crude to highly refined insulating oil starts in the distillation column. The oil is heated and divided into fractions according to boiling point. The fractions at the bottom have the highest boiling point and are refined into bitumen products, while those higher up in the column are more suited to process and transformer oils. After distillation, the next step is hydrotreatment, which transforms the distillates into naphthenic specialty oils. How does it work? The distillate is mixed with hydrogen and heated to over 300°C. This 'treatment' reduces aromatic content and removes sulphur, nitrogen and oxygen, resulting in clean oil – ideal for electrical insulation.