All About Transformer Oil

by Niraj Jayaswal Content Writer

Usually, when we think about the basic components of a transformer, the first things and foremost things which come to our mind are the primary and secondary windings, the laminated core, explosion vents, and so on but most of the time we tend to forget how important the insulating materials are for a transformer to work properly and out of these the significant functions and properties of transformer oil are neglected. I have a friend who works on a senior post in a top-rated transformer repair company in noida, she tells me that for any transformer to work properly, it is important to make sure that the optimal quantities and quality of transformer oil is provided in it composition or else the output value will deteriorate affecting the efficiency of the transformer in to and the susceptibility of defects will increase. An important thing to note is that the transformer oil area primarily used in oil-filled power transformers whereas dry transformers work on different mechanisms.

Oil-filled power transformers use transformer oil as an insulating material to cover the laminated core and both primary and secondary windings of the transformers for their conservation against the temperature changes. The institutions of power transformer repair also focus on the use of transformer oil for separating the atmospheric oxygen from the cellulose made paper insulation.

Transformer oil is chosen after it fits certain categories. Let us look in details what are those properties:

1. Acidity

Good transformer oils do not have high acidic levels. Often measured with acidity tests, transformer oils when free from acidic content are good insulators of windings of the transformer otherwise the acidic conditions of the transformer oil can affect the insulation properties of the paper and even cause rusting of iron by incrementing the oxidation process in the oil.

2. Breakdown voltage (Dielectric Strength)

An important determinant for good transformer oil, the high breakdown voltage is associated with clean and dry transformer oils. Regular cleansing of transformer oil is recommended to improve its dielectric strength.

3. Dielectric dissipation factor

Also known as loss factor, the dielectric dissipation factor of the transformer oil is measured by tan delta test to measure the loss-rate energy.

4. Flash point

The high flash point makes transformer oil less vulnerable to faults which originate from the rise in temperature. Experts recommend that good transformer oil should high flash point or else progress of ignition in the transformer would be easy.

5. Interfacial tension

If a transformer oil is good and new, it would have high interfacial tension which is the measure of the attractive molecular force between the elements of oil and water. Regular tests of the oxidation process in the transformer oil should be carried to make sure that the value of interfacial tension is maintained high since oxidation is indirectly proportional to interfacial tension.

6. Pour point

Paraffin-based transformer oil has a higher pour point than Naphtha based transformer oil and that is why the former is more commonly used in areas with warmer climates.

7. Specific resistance

At 90°C, the specific resistance of transformer oil is recommended to be 35*1012 ohm-cm whereas 1500*1012 ohm-cm should be the specific resistance at 27°C.

8. Viscosity

Transformer oil should be viscous enough to offer minimum resistance to the conventional flow of oil which is why good transformer oils have low viscosity.

9. Water content

It is important to make sure that the transformer oil does not have undesirable levels of moisture because it not only interferes with the dielectric properties but it also does not function properly in terms of insulting the cellulose-based paper. As per the recommendation of the IS-335(1993), transformer oil should not exceed the limit of 50 ppm moisture content.

In India, the well-established and experienced transformers repair and maintenance service, recommend Paraffin based transformer oil in terms of cost-effectiveness because it is easily available in the subcontinent and secondly, its disadvantage of high pour point is not experienced because of the warm climate of the country. Paraffin-based transformer oil is not preferred in cases because its lower oxidation rate obstructs the cooling system of the transformer by precipitating the insoluble sludge at the bottom of the transformer's tank.

In countries where the climate is cold, every transformer repair service of the best kind prefers Naphtha based transformer oil because its oxidation rate is higher than that of Paraffin based transformer oil. Its resultant impact on the cooling system of the transformer is negligible making it a better alternative to the interference caused by Paraffin based transformer oil.