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Types of transformer oil – Testing, Types & Properties

Transformer oil is used in electrical power transformers due to its properties, such as high insulation, stability at higher temperatures, dielectric strength, etc.

Types of transformer oil

It mainly works as a cooling agent and an insulator. In this article, we discuss transformer oil and its types.

What is transformer oil? 

Transformer oil is a special type of oil with excellent insulating properties. Therefore, it is also known as insulating oil. Electrical power transformers use this oil to insulate, prevent arcing and dissipate the transformer’s heat.  Transformer oil is highly stable even at high temperatures. 

Reasons why transformer oil is used in power transformers 

  • Insulating oil protects the transformer’s main core and the winding – as these two are entirely immersed in the oil. The oil also acts as insulation, stopping oxidation reactions and not letting the winding come in contact with oxygen. 
  • Insulating oil keeps the transformer cool from the inside when the transformer is operational by absorbing the excess heat. 

Different types of transformer oil

Mainly two types of transformer oil are used in transformers, namely:  

1. Naphthenic oil

Naphthenic oil is easily oxidizable as compared to paraffinic oil. The product of oxidation – the sludge in the naphthenic oil is more soluble than the sludge from the paraffinic oil. That is how the naphtha-oil-based sludge does not precipitate at the bottom of the transformer, not disturbing the transformer’s cooling system. 

2. Paraffinic oil 

The oxidation product is insoluble and precipitates at the bottom of the tank, though paraffinic oil has a lower oxidation rate than naphthenic oil. The sludge acts as an obstruction to the transformer’s cooling system. 

Parameters of transformer oil

Here are some of the parameters to check the serviceability of the transformer oil: 
  • Electrical parameters

Dielectric strength, specific resistance, and dielectric dissipation factor. 
  • Chemical parameters 

Water content, sludge content and acidity.
  • Physical parameters

Viscosity, interfacial tension, flash point and pour point. 

Why is transformer oil testing necessary?

Transformer oil testing is necessary because:
  • It determines important electrical properties of transformer oil 
  • It detects if regeneration or filtration is required 
  • It helps reduce oil costs and enhances component life 
  • It prevents failures and maximizes safety          

Is transformer oil harmful?

Continued exposure to transformer oil can cause skin dryness or crack. If it comes in contact with the eye, it may cause temporary eye irritation. Prolonged contact with used oil may cause severe skin diseases like skin cancer and dermatitis.  Therefore, take precautions while using the oil, remove contaminated clothing, and wash your skin with soap and water. Get medical assistance if any discomfort continues. 

Bottom line

In conclusion, the oil used in the transformer is a key element in checking the physical condition of the unit. The mineral-based oil is used in various transformers because of its dielectric strength and electrical properties.  If you are looking for transformer oil testing in Vadodara, we can help you with the service. For more information, visit us at Laxmi Associates