What is Transformer Oil: Types & Its Testing?

The oil used in the transformer is a key element to check the physical condition of the unit. In the last five decades in India, there is a drastic change in production technology. The mineral-based oil like transformer oil is frequently used in different types of transformers for its dielectric strength as well as electrical properties. The oil used in the transformer works like a cooling agent & an insulator. This article discusses an overview of what is transformer oil, its functions, different types, properties, testing, and factors to test.

What is Transformer Oil?

Definition: The transformer oil can be defined as a special kind of oil that has outstanding electrical insulating properties. It is also known as insulating oil. At high temperature, this is stable, and it is used in electrical power transformers to prevent arcing, dissolve the heat of the transformer. So, this kind of oil acts as a coolant protects the windings and core of the transformer because these two are submerged within the oil. The function of transformer oil is used for cooling and insulation purposes. We know that there are different kinds of materials available which have dissimilar dielectric strength. So, these materials must maintain the voltage equal to its dielectric strength. For instance, if the voltage of the material is enhanced over the specific dielectric strength of the material, then the current flow will be there throughout it. This oil absorbs the moisture within nature very quickly. The oil dielectric strength will get deteriorated by the absorption of the dampness. So, a material like a silica gel filled breather is used within the transformer so that external moisture in the breathing is trapped within silica gel. The main functions of transformer oil are coolant and insulator.


The primary function of this is as a coolant. The designing of transformer coils can be done with copper that carries high current so that these coils will become hot. It is an excellent heat conductor, so by using this, the temperature of the copper coils can be reduced. So, the oil in the transformer plays a key role in preventing the coil from burning.


It works as an insulator. It includes high dielectric strength to resist with a high voltage. This is the reason it is used.

All samples are taken in line with our oil sampling procedure by trained engineers and a quick turnaround guaranteed. as an insulator within the transformer.

Why Transformer Oil Testing is Important?

  • It determines important electrical properties
  • Recognizes if particular oil is appropriate for future use
  • Notice whether filtration/ regeneration is required
  • It decreases oil costs
  • Component life can be enhanced
  • Untimely failures can be prevented
  • Exploit safety


Testing of transformer oil is mandatory in yearly once for its maintenance. Early testing will set up a bottom line for contrast & yearly testing will design any changes inside the transformer. The transformer quality can be performed through the following tests.

  • Dielectric Strength
  • Dissolved Gas Analysis
  • Moisture
  • Sludge Test
  • Acidity
  • Viscosity
  • Pour Point
  • Interfacial Tension
  • Flash Point
  • Oxidation Stability Test
  • Resistivity

The faults which occur while testing include the following.

  • Corona Discharge Fault: When low energy discharges then it will generate hydrogen, methane minor quantities of ethane & ethylene.
  • Arcing Acetylene Fault: In this fault, huge amounts of acetylene/ hydrogen/small amounts of methane & methylene can be generated.
  • Overheated Cellulose Fault: Whenever the cellulose is excited, then it will generate carbon monoxide
  • Overheated Oil Fault: Overheating oil generates ethylene & methane

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We take great pleasure from our history of customer satisfaction and the fact that our engineers have been around long enough to give the old school service and values that really puts customers first, which we feel is lacking within the industry, without compromising on new regulated guidelines.

Replacement of 500kVA Transformer

posted: 12-11-2021

Out with the old and in with the new!

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