Insulating oil sampling

Transformer oil deterioration and sludge formation are two of the major concerns confronting the transformer operators with regards to the insulating oil. Therefore, the key to predictive maintenance is annual oil testing.

The primary purpose of annual oil testing is to pinpoint the condition of the transformer’s insulation system so that it will operate in sludge-free range.

The normal aging of transformer oil creates sludge which appears earlier in life if the transformer is heavily loaded, running hot, abused or neglected. The presence of moisture and oxygen in the oil will accelerate it’s formation.


Transformer oil analysis is a very powerful and useful tool in understanding the technical state of the transformer.

•  Interfacial tension, color and neutralization value provide important information about the oil status

•  The water content together with the temperature records can provide data on the degree of wetting of the oil and indirectly the water content in the solid insulation

•  Dissolved Gas Analysis (DGA) is a very sensitive tool for detecting a wide range of incipient defects that can influence decisions on the operation of the transformer

•  Furan compounds are by-products of paper degradation, and their determination provides information on mechanical strength and local overheating of paper insulation

•  The contents of corrosive sulphides, particles and metals dissolved in oil provide information about the unusual conditions that may exist in a transformer. It also helps to understand the source of a problem or help clarify the problems identified by other methods


Several things are required to sample the oil:
•  A proper sampling technique
•  Dry and clean container
•  Training and awareness regarding the importance of this action