What is Transformer Oil | Properties of Transformer Oil | Types of Transformer Oil | Testing of Transformer Oil

Just as the human body needs blood, the oil in the transformer is an extremely important element due to which its physical condition can be checked. India has seen dramatic changes in production technology over the last several years. Oil-based transformers are frequently used in a wide variety of transformers for their dielectric power and electrical properties.

The oil used in the transformer provides cooling to it and acts as an insulator. In today’s article, we will look at what transformer oil is and its function, properties, different types, and its testing.

Also Read: What is an Oil Circuit Breaker | Construction | Working Principle | Types Of Oil Circuit Breaker

What is Transformer Oil?

Definition: The oil used in a transformer can be defined as a specific type of oil. It has more electrical insulating properties compared to other oils. This oil is also known as insulator oil. Stable at high temperatures and is used in electrical power transformers. So that curry can prevent arcing and keep the transformer cool.

That is why this type of oil acts as a coolant in the transformer so that the winding and core of the transformer can be protected. This is why it is completely immersed in oil.

Transformer Oil

The main function of a transformer is to keep you cool and is used for insulation purposes. We know that the dielectric power of each of the materials used in a transformer is different. Therefore each material must maintain the same voltage of its own dielectric power.

If the voltage exceeds the dielectric power of the material then the current will be there That is why it will absorb the amount of moisture in the atmosphere and the dielectric power of the oil will deteriorate due to the soaked moisture. Materials such as silica gel-filled breaths are used inside the transformer to prevent this type of defect from forming. So that the moisture of the atmosphere stops there and cannot go inside its breath.


The first and foremost function of this is to cool the transformer. As we all know that winding of the transformer is done from copper which has the strength to carry a high electric current. Due to the conduction of this electric current, it gets heated.

This is one of the best heat conductors so using it can easily reduce the temperature of copper and its coils. That is why transformer oil coils play a big role in preventing burns.

Also Read : What is a Conservator Tank of Transformer | Construction And Its Working


It acts as an insulator. It involves high dielectric strength to resist high voltage. This is the reason why it is used as an insulator inside the transformer.

Properties of Transformer Oil: 

  • Transformer oil properties mainly include the following points.
  • Due to its best dielectric properties, there is less loss of power.
  • High result performance.
  • There will be better insulation values ​​between the windings due to higher resistance.
  • Evaporation losses will be reduced due to thermal stability and higher flashpoints.
  • The chemical properties of transformer oil mainly include properties like acidity, water content.
  • The temperature range is wide.

Also Read: What is a 4 Point Starter | Working Principle | Diagram & Its Applications

Types of Transformer Oil:

There are two types of transformer oil which are as follows:

Sr. No. Types of Transformer Oil
#1. Naphthenic Oil
#2. Paraffinic Oil

#1. Naphthenic Oil:

Mineral insulating oils are made from special crudes that contain extremely low N-paraffin called wax. The pouring point of this oil is lower than that of the paraffinic type due to the wax content. The boiling point of this oil is about 425 ° C. This makes harvesting more easily compared to other oils.

Oxidation products are soluble in oils. Corrosion of paraffin-based crudes produces an incredible sludge to increase viscosity. It will therefore reduce heat transfer, service life, and the ability to overheat.

#2. Paraffinic Oil:

Mineral insulating oils derived from special crude oil contain only very large amounts of N-paraffin. Due to the high wax content, the pouring point of this oil is higher than that of the nephithic type. The boiling point of this type of oil is about 530 C.

This oil is low in oxidation. Oxidation products are insoluble in oils.

Why Transformer Oil Testing is Important?

Transformer Oil Filtering

Its testing becomes important for the following reasons.

  • It determines the important electrical properties.
  • Whether it is suitable for future transformers.
  • It reduces oil costs.
  • Premature failure can be prevented.
  • Safety exploitation.

Testing of  Transformer Oil:

For proper maintenance of the transformer, it is mandatory to test the transformer oil once a year. The initial test will set a bottom line for contradictions and the annual test will form any changes inside the transformer.

Transformer oil quality can be done by the following tests:

  • Humidity.
  • Flashpoint.
  • Acidity.
  • Pour points.
  • Interfacial tension.
  • Oxidation stability test.
  • Resistance.
  • Dielectric Strength.

Testing factors:

The following factors need to be tested when testing:

  • Fluid power factor.
  • Acid number.
  • Visual examination.
  • The breakdown voltage of the dielectric.
  • Specific resistance.
  • Interlingual stress.

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