Transformer oil testing is performed for both new products and for regenerated oil. Water content is a part of the testing is both cases.
Knowing the amount of water in the oil is indicative of its quality, and provides information on the causes of oil and solid insulation dielectric strength deterioration.
The highest allowed concentration of water in transformer oil depends on the type of equipment; on average, no more than 10-20 ppm (grams per ton) is allowed. Detecting such a small amount of water is not simple, and the methods used for the testing must be highly precise and sensitive. Higher concentrations of water may cause transformer failure, so using a transformer oil dehydration machine is a mandatory measure.
Some of the most common methods of measuring the amount of water in the transformer oil are:
filtration;
gas chromatography;
mass spectrometry;
the calcium hydride method;
photoacoustic spectroscopy.