Methanol marker for the thermal performance qualification of power transformers

The new chemical markers for the transformer insulating paper aging are characterized by their occurrence after the first chain scissions of the cellulose solid insulation. Furthermore, one of the major concerns for transformers users is the knowledge of the thermal performance of their new equipment. Nowadays, the standard heat run test remains the only mean to validate the thermal design in the process of the qualification of new power transformers. In addition to this test, the analysis of dissolved gases are achieved but they are not dedicated to the detection of cellulose degradation. The factory acceptance tests (FAT) and mainly the heat run test, give the opportunity to verify whether the methanol production in oil may bring some additional information about the quality of the thermal design. In this paper we report the experience performed during qualification testing at the factory in which we examined whether these new markers provide a new insight. During the factory heat run test of some transformers including GSUs, we collected samples of oil to carry out physico-chemical analyzes, and some key points are derived from these investigations. Methanol production is generally detectable during the heat run tests and seems consistent with the measurement of the hot spots in the windings. Singular behavior of some units can be detected through the measurement results of methanol marker concentration in oil. The sensitivity of methanol during temperature rise test is an interesting approach and could be promising as a complement to conventional dissolved gas analysis. Further investigations are also identified, like the impact of the duration of the test or the influence of the drying process of the active part.