Abstract: In order to test the accuracy of the on-line monitoring devices for dissolved gases in transformer oil, calibration with the standard oil has become the mainstream method. At present, there are mainly two standard oil preparation method, i.e., mixed standard gases method and single standard gas method. In this paper, precautions for application are proposed regarding the mathematical models related to the two methods,. From the comparison between the two preparation methods and the corresponding mathematical models, it is concluded that the single standard gas is more advantageous. Based on the mathematical model of single standard gas method, the automatic standard oil preparation device(automatic oil distribution instrument) is improved and tested through the preparation of the dissolved gases of transformer oil. The study results show that the improved automatic oil distribution instrument is of high accuracy with the oil preparation error of less than ±10%. The piston type stainless steel cylinder is proved to have better performance in oil storage. The concentration stability of the standard oil stored in this type of cylinder can completely meet the inspection requirements.

Key words: transformer oil, oil-dissolved gas, standard oil, mathematical model, single standard gas, mixed standard gases