(Transformer) Oil Chemical Tests

Oil in Power or Main Transformers serves as a cooling medium and insulation for the windings. The main purpose of the oil chemical tests is to determine and monitor the chemical properties of oil, which is very essential for its purpose, since failure in such chemical properties could be disastrous for the transformer itself.
The tests recommended are the following:

Neutralization (Acid Number): ASTM D-974
This test measures the neutralization number. When oil oxidizes in a transformer, acid and sludge are produced, as well as water. A severe increase in neutralization number can be detrimental to the insulation system. New oil specification is 0.03 or less.

Interfacial Tension (IFT): ASTM D-971
ASTM D-971 is very sensitive in detecting oil-soluble polar contaminants such as acids and sludges formed from the oxidation of transformer oil. The more contaminants in the oil, the lower the interfacial tension. New oil specification is 40 dyne/cm minimum.

Moisture Content: ASTM D-1533
New oil specification is less than 35 ppm. This is a very important test as moisture affects the dielectric properties of the oil.

Power Factor: ASTM D-924
This test measures the leakage current that passes through oil. A very sensitive indicator of deterioration products, it has become one of the more useful tests in the industry. The greater the power factor, the more polar the contamination in the oil.

Colour and Visual: ASTM D-1524
This test checks turbidity, cloudiness, suspended particles and colour. New oil has a colour rating of 0.5 and is bright and clear.