The statistical distribution of the DGA data of transformers and its application

Dissolved gas analysis (DGA) is one of the most widely used diagnostic tools for detecting faults and evaluating the condition in oil-impregnated power transformers. However, interpretation of DGA results is often complex and should always be done with care, and it is claimed to get local criterion from local transformers. The concentration values of dissolved gases in 760 transformers, from Guangzhou area of China, were processed to get their statistic distribution, by hypotheses of normal distribution, logarithmic normal distribution and Weibull distribution and Kolmogorov-Smirnov Test. Furthermore, the best theoretical distribution functions were established for each type of dissolved gas in 110 kV transformers and 220 kV transformers respectively, and the local typical values and alarm values were obtained from them. Finally, the local typical values were contrasted with that in the IEC standard and the national standard. And three problems were discussed.