Summary of transformer oil tests and their test objectives
(1) ASTM D971, Interfacial tension (IFT)
The IFT test measures the presence of soluble contaminants and oxidation products. A decreasing value indicates an increase in contaminants and/or oxidation products within the oil.
(2) ASTM D974, Acid number
The acid neutralization number is a measure of the amount of acid materials present in the oil. As the transformer ages, the oil will oxidize and increase in acidity. The acid value can also increase from contamination of other foreign material such as paint, varnish, etc.
(3) ASTM D1533, Moisture
The Karl Fisher Moisture Test measures water ppm within the transformer oil. ** Note it does not measure the water content in the paper insulation.
(4) ASTM D924, Power factor
The power factor test measures the dielectric losses of the oil, or energy that is dissipated as heat. A low value indicates low losses. It is a useful test for measuring changes within the oil resulting from contamination or deterioration.
(5) ASTM D877/ASTM D1816, Dielectric breakdown voltage The dielectric test measures the ability of the oil to withstand electric stress without failure. The higher the value, the lower the presence of contaminants such as water, dirt, or other conductive particles.
(6) ASTM D3612, Dissolved gas analysis (DGA)
The DGA test measures various gas ppm levels that are present. Different gasses will dissolve in the oil that indicate various types of thermal and electrical stress occurring within the transformer.
(7) ASTM D1500, Color
The color test is a simple test that indicates oil quality. The higher the color number is, the higher the probability of contamination or deterioration of the oil.
(8) EPA 8082, PCB
Test the PCB ppm level of the oil.
