General:
This test method determines the oxidation stability of mineral insulating (transformer) oils under prescribed accelerated aging conditions. Oxidation stability is measured by the propensity of the oil to form sludge and acid products. The method is applicable to new uninhibited and inhibited mineral oils but is not well defined for used or reclaimed oils.
Precision:
Precision statements are provided at the 95% probability level: Repeatability (same operator, same apparatus): Sludge, wt %: 0.12X
Neutralization value, mg KOH/g: 0.22X
(where X is the average of two determinations).
Multi-laboratory reproducibility criteria are also defined in the full standard. No bias statement is established as results depend solely on the test procedure.
Test:
A test specimen of mineral insulating oil is placed in a glass vessel with a copper catalyst coil. Oxygen is bubbled continuously through the sample while it is maintained at 110 °C for 72 h or 164 h. After aging, the oil is evaluated for the amount of sludge formed (by filtration and weighing) and total acidity (neutralization value). Results are reported as weight percent sludge and mg KOH/g oil.