In each power utility, a numbers of different tests are

conducted for evaluating the quality of transformer oil. The

information provided by each measurement and analysis

techniques has varying degree of significance towards the

identification of quality of oil. Consequently, it is important to

understand the accuracy of different interpretations. In this

paper, Dissolved Gas in oil Analysis (DGA), one of the most

important tools for transformer fault diagnosis is investigated. In

a case study different DGA diagnosis methods are compared at

different rated voltage levels and based on the obtained results

accuracy of each method is calculated. The examined dataset