Criteria revision of dissolved gas analysis for oil-filled transformers in Korea

The story on revising criteria of dissolved gases analysis (DGA) at KEPCO was introduced. Because of differences in operating environments, construction type, oil volume, and other factors, the interpretative criteria of DGA at KEPCO should be different from other standards such as IEC-60599, or Rogers and Doernenburg. We tried to improve efficiency of DGA by considering accumulated data during twenty-five years. To establish the most appropriate criteria, the DGA results were collected from healthy power transformers as well as transformers which have an incipient fault. The criteria were revised newly using cumulative distribution of concentration of 3,585 healthy power transformers. Although the criteria are revised strictly, work load doesn´t increase by controlling analysis interval and condition level.