Why do we need to check Transformer Oil ?
Issue Time:2016-09-23

                                       Why do we need to check Transformer Oil ?

   Transformer oil is an insulator betweenthe metal parts of the transformer and the wiring within the tank. Over time,the oil can be contaminated with moisture or create combustible gases. Bysampling and testing that oil, we can plan repairing or replacing thetransformer before a failure occurs.

MaintenanceSchedule for Oil Filled Power Transformers

Maintenance or Test

Recommended Interval



Transformer physical inspection




Leakage of oil and reading of MOG (Magnetic Oil Gage) of tanks


In case of unsatisfactory oil level in the MOG, oil to be filled in transformer and also the transformer tank to be checked for oil leakage. If oil leakage is found take required action to plug the leakage. If silica gel becomes pinkish, it should be replaced.


Dielectric strength test (BDV) and moisture content (PPM).



A dielectric strength is a measure of the voltage which is conducted by the transformer oil. At times it is the presence of contaminants which conduct electricity faster than the oil which in turn lowers the dielectric breakdown voltage

Neutralization test



This test which is carried out to ascertain the level of acid which is present in the oil. When oxidation occurs in the transformer oil, it leads to build-up of acid.

Dissolved Gas Analysis Test (DGA)

Annually for 132 KV transformer, once in 2 years for the transformer below 132 KV transformer and in 2 years interval for the transformer above 132 KV transformer.


It helps to analyze the gases which are present in the transformer oil.

Bushings– check of oil level



If it is required, the oil to be filled in the bushing up to correct level. Oil filling to be done under shutdown condition.


Bushings –visual inspection




Bushings – visual inspection and cleaning


5 years


Interfacial tension test


This is a test which is carried out to detect the presence of polar compounds such as paint, varnish and paper.

Tan & delta test

One in two years

Finally the presence of water too is measured as water can decrease the dielectric breakdown voltage of the transformer oil

Colour test


This test indicates aging, quality and the presence of contaminants in the transformer oil.

Transformer excitation current test


5 years


Insulating oil   – DGA, physical,

and chemical tests




Top oil and winding thermometer





Oil level indicator operation


5 years


Sudden pressure relay

5 years



So, for getting high performance and long functional life of thetransformer, it is desired to perform various maintenance activities. Yuneng’s  Transformer Oil  Purifier Machine will keep your transformer oil in the best condition, providing with oildegassing, water and solids removal as well as acids reducing. It’s a fantastictransformer life!

Vacuum Transformer Oil Purifier

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