Transformer oil is used to insulate the electrical power in the transformer and for cooling purpose. It is a mixture of mineral oils. The mineral oils are colorless, odorless in nature, and it contains high alkenes from mineral source and petroleum.

The transformer oil insulates the electrical power so it is also called as insulating oil. It is high temperature and stable in nature. It protects the transformer from the direct contact of oxygen. Transformer oil has the property of dielectric strength, thermal conductivity, and chemical stability.

A transformer can provide alternating current to all over the world. Sometimes the transformer gets damage due to the damage of different external equipment in the transformer, or due to the changes in nature of transformer oil.

We make different types of test for transformer oil, Acidity Test of Transformer oil is one of them. We can find how much quantity of acid is contained in transformer oil by this test.

The acid test for Transformer oil:

Cause for test: Sometimes the insulating oil or transformer oil make closer with the air for which it can create a problem for the transformer, like leakage of oil in the tank or in the related pipelines. When it comes closer to the air there will be an oxidation reaction is takes place in the transformer oil, which can be accelerated due to the temperature and catalyst.

Effect of acid in transformation oil: If the acidity of transformer oil is increased then the resistivity of the oil will be decreased. The increase of acidity and decrease of resistivity will be the cause of the destruction of paper used in transformer oil.

To Measure the acidity of insulating oil:

The substances required to measure the insulating oil are Potassium hydroxide, Transformer Oil.

The acidity of insulating oil is 0.3 mg KOH/g. We can experiment this test in a chemistry laboratory.

We can conduct another experiment in a different way by the help of ethyl alcohol, sodium carbonate solution and universal indicator in a test tube.

The principle of acidity test of transformer oil:

The acidity test of transformer oil can be experimented by titration method. Whenever a particular amount of alkali is added with the same amount of insulating oil its nature will be change into acidic, neutral or alkaline. If the added alkali is equal to the required quantity of alkali then it will neutralize the transformer oil. If the added alkali is more than the required amount of alkali to neutralize then the oil will be alkaline. And if the added alkali is less than the required quantity of alkali to neutralize then the oil will be acidic in nature. In neutralizing solution the pH value is 7, if the solution is acidic then the pH value will be 0-6, and if the solution is alkaline then the pH value will be 6-14.

Procedure for the test:

  • Take 1.1 ml of insulating oil in a clean dry test tube through a syringe or dropper.
  • Add 1 gm of ethyl alcohol in the test sample and gently shake it.
  • After shaking add 1 gm of sodium carbonate in the sample.
  • Again shake it well and add 5 drops of universal indicator, in the solution.
  • After the adding of universal indicator, the solution changes its color and the color chart will indicate that how much acid is contained in the insulating oil.


We can measure the acidity of transformer oil by the above process and can find the particular measurement of acidity in the oil through the help of the above color chart. The color chart can indicate how much of acid is present in the transformer oil.


The acidity test of transformer oil is a simple test to detect the acidity of transformer oil. The test can help the transformer from damage.