What is dehydration of Transformer oil?

In which process the moisture can remove from the transformer oil is called as dehydration of transformer oil. In this process, we can eliminate the solid particles, dissolved gases, dissolved water and dried up the moisture and sludge from the transformer oil.

Dehydration method is also used to maintain the temperature of the transformer oil. 75 % of the transformer can fail due to the moisturization in transformer oil. The Centrifuge is another method to filtrate dirt from the transformer oil. Before the filtration of oil in high vacuum transformer oil filtration the oil is mixture with 10% of water and 15% of air.

Importance of dehydration in Transformer Oil:

Dehydration increase the insulating properties of transformer oil. The life of the transformer depends on the quality of the transformer oil. So the oil should be filtrate and dehydration method is important for the transformer.

What is Filtration of Transformer of Transformer Oil?

In which process the oil can be filtered in the help of High vacuum filtration machine is called filtration of transformer oil. It helps to eliminate the solid elements from the oil. There are different types of contaminants in the transformer oil, like solid particles, carbon particles due to the aging of switchgear, sludge, moisture, absorption of air, different types of gases, excess of acid level and etc. Filtration and dehydration of transformer oil can change the life period of the transformer.

Importance of Filtration in transformer oil:

  • Long lasting of transformer
  • Less breakdown in transformer
  • Good working of transformer
  • Improve of insulating properties in oil

The process of filtration in Transformer oil:

  • Rising the temperature of oil: In the first step heat the oil in the temperature of 65°C to extract the water or moisture and gases. The heating process makes the filtration easier due to the decrease of viscosity in oil.
  • Removal of dirt and impurities: All sludge and dirt can be removed in this step. In this step, there are two methods to extract the dirt, by filter candles and by centrifuging action.

By filter candles: By the method of filter candles the transformer oil can be classified by using the classical edge filter or depth type filter. The edge type filter makes the transformer oil cleaned and reused for at least 3-4 times.

By centrifuging action: In this process, we can save the recurring cost of changing filters. Advantages of centrifuging action are no moisture storage in oil, easy to replace with little effort and easily available.

  • Degasification and Transformer Oil: In this process, we can remove gases from the transformer oil. This process ends at the degasification chamber.
Sr. No. Parameter Units Before Filtration After Filtration
1 Break down voltage kV 25 >50-70
2 Removal of moisture ppm 50-100 Up to <5-10
3 Value of neutralization Mg of KOH/g 0.5 <0.1
4 Gas Content %Vol./ Vol. <10% <0.1%


Transformer oil is necessary for insulate the transformer. If the transformer oil is impurity less, then the transformer can be lasting for a long time. Filtration and dehydration of transformer oil are most necessary for the transformer.