Evaluation of mineral insulating oil by rapid small scale oxidation test

Mineral oils are used in transformers as insulants and coolants. The long term performance of theses oils depends on their stability to oxidation of the oil. This characteristics is usually termed as resistance to oxidation process or oxidation stability. To assess oxidation stability of the insulating oils, every manufactured batch or sample is subjected to laboratory tests, by simulating the factors that influence the process of oxidation. One of the popular method followed is the oxidation stability test, where the oil is put to accelerated oxidation process by bubbling zero air over a duration of 164 to 500 hours as per IEC 61125 norms and by Rotating Pressure Vessel Oxidation Test method (RPVOT) as per ASTM D2112. Each of these procedures measure, different parameters to asses the oxidation stability of oil, depending on the test method. Experiments on same sample of insulating oils are also carried out by using a new method called Rapid Small Scale Oxidation Test method (RSSOT) ASTM D7545. The results are compared to assess the suitability of rapid small scale method for analysing the stability of insulation oils. RSSOT method has main advantage of rapid deliverance of test results and small quantity of sample. It is found that the rapid small scale method is comparable to the existing methods of oxidation stability characteristics of the oils.