The acids are organic and nothing like as corrosive as, say, sulphuric acid, but they can cause corrosion and accelerate the degradation of solid insulation. There is, however, a great deal which can be done to reduce oxidation without the use of additives. Firstly by reducing the degree of contact between the oil and air. There are good reasons for not wishing to seal off the oil completely from the external air and these will be identified later. However, in all but the smallest distribution transformers it is economic to provide a conservator. Not only does this reduce the area of contact between the oil and air, but it also ensures that the oil which is in contact with air is at a lower temperature than the bulk oil. Temperature is, of course, an important factor. Each 7