Transformer Oil Composition

Transformer oil is used to insulate the electrical power of a transformer and used to stop the direct contact of oxygen in the transformer. The transformer oil is a combination of mineral oils. It is of two types: Paraffin-based transformer oil and Naphtha-based transformer oil.

1)Paraffin-based Transformer Oil:

Paraffin: Paraffin is a colorless, odorless solid substance which can’t soluble in water and does not easily react with any reagent. It is a member of alkane series and a mixture of hydrocarbons. It is used in waterproofing paper, candle, and for coating and seal.

Paraffin Oil: Paraffin oil is the mixture of alkane hydrocarbons with boiling point (150-300)degree Celcius in liquid form. This oil is mainly used in hygiene oil, cold cream, perfumes, cosmetic substance, candle, and in medical purpose.

2) Naphtha-based Transformer Oil:

Naphtha Oil: Naphtha Oil is a flammable or burnable, liquid hydrocarbon mixture. Naphtha is produced from the natural gas condensates, petroleum distillate, distillation of peats and coal tars.

Difference between paraffin-based transformer oil and Naphtha-based transformer oil:

Paraffin-based transformer oil:

  • Paraffin oil gets less oxidized than Naphtha oil.
  • Paraffin is less soluble than Naphtha oil.
  • The sludge of Paraffin oil does not precipitate at the bottom of the oil tank and disturb the transformer cooling system.
  • The use of Paraffin oil is more in India because of its availability.

Naphtha-based transformer oil:

  • Naphtha oil gets more oxidized than Paraffin oil.
  • Naphtha is more soluble than Paraffin oil.
  • The sludge of Naphtha oil does not precipitate in the bottom of the transformer and does not disturb the transformer cooling system.
  • The use of Naphtha oil is less than Paraffin oil because it is not easily available in our country.

Effect of hydrocarbon in the transformer oil:

Hydrocarbon helps to derive or making petroleum for transformer oils and identified by the very low values of tan ẟ at 50 Hz and temperatures from (20-125)℃. Ional (2,6-di-tert-butyl-4-methylphynol) is used in a fraction of monocyclic aromatic hydrocarbons isolated from a transformer oil distillate. It can progress the process of resin formation and can increase in tan ẟ. The fraction of isolated aromatic hydrocarbon has higher conductivity than the Paraffinic and Naphthenic fraction.

Chemical Properties of Transformer Oil:

1.Neutralization Number: Neutralization number is the number of a milligram of Potassium hydroxide to neutralize completely acids present in 1 gm of the insulating oil. The cause of neutralization in transformer oil is due to the aging of oxidation. The effect of neutralization number corrosion of various parts of the transformer, insulation degradation, and lower strength of electric.

2.Oxidation Stability: Oxidation Stability is the chemical reaction due to the combination of lubricating oil and oxygen. Moisture is the cause of oxidation stability. In the absence of oxidation stability, metal corrosion will minimize the life of the transformer.

3.Moisture: A small amount of water which makes something wet or moist is called moisture. Chemical reaction and breathing action are the cause of moisture. The absence of moisture can decrease the electric strength (BDV), and resistivity of dissipation factor.

4.Dissolved Gases: It is the measurement of dissolved gases produced in the oil due to the decomposition of oil. Thermal degradation arcing and partial discharge are the cause of dissolved gases. Effects of dissolved gases are partial discharge, low energy discharge, arching, and high temperature.


At last, we can conclude that the transformer oil is combined with different types of component. Transformer oils are mineral oils, dissolved gases, Paraffin, Naphtha, and hydrocarbon.