Abstract: To ensure the accuracy of the field test results, the standard oil dispensing system of dissolved gases in transformer oil is developed. In this paper, the working principle of the system is introduced and the structures of the atmospheric pressure as well as the standard oil dispensing system are presented. In this system the absolute pressure is applied to quantitatively dispense the mixed gas such that the difficulties of large deviation between the target concentration and the practical concentration of the prepared mixed gas is overcome. Hence the accuracy of the prepared standard oil can be guaranteed. For the first time the negative pressure method is used to compound gases. By changing the pressures, the mixed gas consisting of any combinations and concentrations of components can be prepared. This method is also characterized by high stability, easy storage and straightforward preparation procedures. The oil data quantity value can remain stable for more than 180 days with the uncertainty degree less than 10% if it is preserved in the special storage device. The standard oil prepared by this system meets the requirements of the national standard for secondary substance, and is suitable for transportation in the whole country.

Key words: transformer oil, standard oil, negative pressure preparation, chromatograph analysis, quantity stability