What is Transformer oil and It’s uses, types and properties

An electrical transformer plays very important role for delivering electricity efficiently from power plants to our homes. The complex system of transformer includes windings, cores and coils which converts the voltage levels for smooth transmission of electricity.

However, the whole process generates substantial heat and electrical stress which needs to better treatment for smooth functioning.So, transformer oil is used in transformers primarily to provide Insulation and Cooling. Although it has few more objectives which we will discuss further.

Transformer oil is mostly used in transformers but it is also used in other equipment to provide electrical insulation and cooling.

The transformer oil is normally obtained from fractional distillation and subsequent treatment like refining and processing of crude oil. So, it is basically a mineral oil and we will discuss its types later in this post.

Use of transformer oil

Transformer oil serves few main objectives as follows:

  1. It provides insulation between high voltage components such as windings and coils. Due to its good insulation properties, the distance between the windings can be made small. It prevents short circuits and ensures safe operations.
  2. It provides cooling  to the transformer by dissipating the heat generated in windings and core of transformer. It acts as coolant and prevents overheating.
  3. It prevents corrosion between the various metal parts of transformer and maintains the health of transformer in good condition.
  4. Transformer oil also helps to sense the faults inside the transformer. Buchholz relay operation depends upon transformer oil. To know about Buchholz relay and its operation you can read here.
  5. It also provides oxidation resistance to transformer components and increase the life.

Overall, a Transformer oil provides so much objectives which helps in efficient functioning of transformer.

Characteristics or Properties of Transformer oil

  1. High dielectric strength: Transformer oil has high dielectric strength which makes it good to withstand high voltages without breaking down or allow electric discharge.

The voltage at which sparking occurs is called as breakdown voltage of transformer oil. It is measured by putting two electrodes which are immersed in oil at some specific gap.

Minimum breakdown voltage at which transformer can safely use is 30kV.

  • Low viscosity : viscosity refers to fluid’s resistance to flow. Transformer oil has low viscosity.
  • Low pour point: the pour point is the lowest point at which the liquid can still flow. It is very necessary to ensure that oil remains fluid even in cold conditions for proper functioning.
  • High flash point: flash point is the temperature at which oil vapour can ignite when exposed to open flame. Hence, the flash point must be high.
  • Oxidation stability: oxidation resistance of a transformer oil should be good as oxidation can lead to formation of sludge (wax content) and degradation of oil properties over time.
  • Free from moisture: Transformer oil must be free from moisture content because it will decrease the breakdown voltage and also affects the quality of oil.

Types of transformer oil

At present there are two types of transformer oil as follows:

  1. Mineral oil
  2. Bio based oil

The bio-based oil is very good in all aspects but is very costly and rare in amount. That is why it’s use is very limited to only important areas like remote locations and underground transformer operations (coal mines etc.). Hence, we will only focus on mineral oil because it is used widely all over the world.

Mineral oil

As I already said that this oil is extracted from crude oil by subsequent refining and processing. Mineral oil is composed of hydrocarbons which are organic compounds made up of hydrogen and carbon atoms. Mineral oil has two main types which are used as transformer oil.

  1. Paraffinic based oil
  2. Naphthenic based oil

Paraffinic transformer oil

This oil contains paraffin hydrocarbon compounds. Paraffin based oil has good electrical insulation properties, heat transfer capabilities and high oxidation stability. It also has low viscosity.

Although, the oxidation stability of paraffinic transformer oil is good but the content formed due to oxidation is insoluble with the oil and it settles down at the bottom as sludge (wax type semi-solid). This affects the overall health of oil.

The pour point of paraffinic based transformer oil is high, it means that it will find difficulty to flow at cold climatic conditions. But, In India no such problem occurs due to its warm climatic conditions.

Naphthenic transformer oil

The mineral oil higher proportions of naphthenic hydrocarbons make naphthenic transformer oil.

Naphthenic based transformer oil has excellent low temperature properties or we can say that the pour point of this oil is very low, which makes it very suitable even in cold climatic conditions.

Good electrical insulation, high thermal stability and low viscosity are some more features of this oil.

It provides less oxidation resistance than paraffinic based oil but the content formed after oxidation is soluble with the oil and does not settle down. This makes it more efficient.

After the brief discussion for both oil we can conclude that naphthenic based transformer oil has major advantages over the paraffinic based oil.

In India like countries where temperature does not have much impact, the paraffinic based oil is more in use to its low cost.

This is all about transformer oil: uses, properties and its types. I hope all your queries regarding this topic are now cleared.

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