Transformer oil is a mineral (clean hydrocarbon) oil, which is obtained by refining crude petroleum. It has the following purposes:
- It provides additional insulation.
- It carries away the heat generated in the core and the coils.
- It protects the paper from dirt and moisture.
Transformer oil has the following properties:
- High dielectric strength.
- Low viscosity to provide heat transfer.
- Good resistance to emulsion.
- It must be free from inorganic acid, alkali and corrosive sulphur.
- It must have high flash point.
- It must be free from sludging under normal operating conditions.
The most important factors are:
- Operating temperature.
- Atmospheric conditions, particularly inside stations.
- Electric strength.
- Moisture and other contamination.
- Sludge formation.