What is Transformer Oil?


Transformer Oil is used for insulation and cooling of transformer.

The oil should be perfectly free from moisture as it will reduce the insulation strength considerably.

The insulation property of transformer oil is further reduced due to formation of sludge which is an oxidation product and its formation is accelerated by the contact of oil with air and temperature.

Transformer Oil.jpg

Transformer Oil Tin

Sludge is also formed due to the presence of acids and alcohols. To minimize the oxidation, transformer oil should be exposed to air to a minimum time possible. The sludge formation reduces heat transfer, blocks the ducts and increases the operating temperature. To prevent moisture entering the oil, the whole apparatus is made air tight and calcium chloride silica gel filters are used. Para oxidiphenylantine having a melting point of 65oC are used as an admixture to slow down the ageing of oils.


  1. Its dielectric strength s 40kv/mm/min
  2. Its flash point is 160oC
  3. Sludge value percentage is 1.2
  4. Its specific gravity is 0.88
  5. Its dielectric constant is 22.
  6. Its pour point is -40 oC

Uses: Transformer oil is used in transformers, switchgears and power factor capacitors.