scope:

This method describes a test for evaluating the oxidation stability of insulating liquids in the 84 delivered state under accelerated conditions regardless of whether or not antioxidant 85 additives are present. The method can be used for measuring the induction period, the 86 test shall be continued until the volatile acidity significantly exceeds 0,10 mg KOH/g in 87 case of mineral oils. This value may be significantly higher in case of ester liquids. 88 The insulating liquid sample is maintained at 120 °C in the presence of a solid copper 89 catalyst whilst bubbling air at a constant flow. The degree of oxidation stability is 90 estimated by measurement of volatile acidity, soluble acidity, sludge, dielectric dissipation 91 factor or from the time to develop a given amount of volatile acidity (induction period). 92 In the informative Annex B a test method for evaluating the oxidation stability of inhibited 93 mineral insulating oils in the delivered state by measurement of the induction period is 94 described. The method is only intended for testing the continuity of oil supplies. The results 95 do not necessarily provide information on the performance in service. The oil sample is 96 maintained at 120°C in the presence of a solid copper catalyst whilst bubbling through a 97 constant flow of oxygen. The degree of oxidation stability is estimated by the time 98 taken by the oil to develop a determined amount of volatile acidity. Additional criteria 99 such as soluble and volatile acidities, sludge and dielectric dissipation factor may also be 100 determined after a specified duration. 101 In the informative Annex C a test method intended to simulate the thermal-oxidation 102 behaviour of ester insulating liquids (headspace of air at 150°C for 164h) is described. 103 Additional test methods e. g. IEC TR 62036 based on differential scanning calorimetry may 104 also be used as screening tests, but are not part of this standard.