Abstract: There was welding seam leakage fault in No.1 unit main transformer Cphase oil reservoir of Inner Mongolia Huadian Baotou Power Generation Corporation Limited. When No.1 unit was overhauled, the gas cutting and repair welding with oil filled for the oil reservoir had been carried out, and the process was introduced in this paper. Because of the field treatment with oil filled, the tedious work of the oil discharging, the cover hanging and others were avoided, and the high cost for returning the main transformer to the manufacturer to repair was eliminated, and the repair period also was shortened.

Key words: main transformer, oil reservoir leakage, treatment with oil filled, gas cutting, repair welding