Abstract A malfunction that the concentration of hydrogen in the oil exceeds the standard is found in the production process 35kV transformers. Usually, such common malfunctions are insignificant, but they still affect lifetime of transformer. Through testing many procedures of production, the principal cause is determined to be the free water in oil. After finding the source of the water, the production process is optimized and the problem is solved.
2022, Vol. 23 
