Physical Parameters of Transformer Oil
(1) Inter Facial Tension of Transformer Oil
Inter facial tension between the water and oil interface is the way to measure molecular attractive force between water and oil. It is measured in Dyne/cm or mili-Newton/meter. Inter facial tension is exactly useful for determining the presence of polar contaminants and oil decay products. Good new oil generally exhibits high inter facial tension. oil oxidation contaminants lower the IFT.
(2) Flash Point of Transformer Oil
Flash point of transformer oil is the temperature at which oil gives enough vapors to produce a flammable mixture with air. This mixture gives momentary flash on application of flame under standard condition. Flash point is important because it specifies the chances of fire hazard in the transformer. So it is desirable to have very high flash point of transformer oil. In general it is more than 140°(>10).
(3) Pour Point of Transformer Oil
It is the minimum temperature at which oil just start to flow under standard test condition. Pour point of transformer oil is an important property mainly at the places where climate is extremely cold. If the oil temperature falls bellow the pour point, transformer oil stops convection flowing and obstruct cooling in transformer. Paraffin based oil has higher value of pour point, compared to Naphtha based oil, but in India like country, it does not effect the use of Paraffin oil due tits warm climate condition. Pour Point of transformer oil mainly depends upon wax content in the oil. As Paraffin based oil has more wax content, it has higher pour point.
(4) Viscosity of Transformer Oil
In few wards, viscosity of transformer oil can be said that viscosity is the resistance of flow, at normal condition. Obviously resistance to flow of transformer oil means obstruction of convection circulation of oil inside the transformer. A good oil should have low viscosity so that it offers less resistance to the convectional flow of oil thereby not affecting the cooling of transformer. Low viscosity of transformer oil is essential, but it is equally important that, the viscosity of oil should increase as less as possible with decrease in temperature. Every liquid becomes more viscous if temperature decreases.
