the system (multi-component principle) is a product for on-line monitoring of multi-component gas dissolved in transformer oil based on the gas chromatography technology. it can detect the content of all components of the gas dissolved in transformer oil, such as h2、co、co2、ch4、c2h2、c2h4、c2h6, according to the determined cycle. and through an expert system, it determines whether there is a latent fault, overheating fault or discharge fault, and gives sound and light alarm according to the set alarm value.