Alternate and Effective Dissolved Gas Interpretation to Understand the Transformer Incipient Faults

Various techniques of fault diagnosis in oil immersed power transformers have been utilized for the last two decades and are well reported in the literature. The traditional and widely accepted dissolved gas analysis (DGA) methods include IEC gas ratio code, IEEE Key gas, Doernenburg ratios, and the Duval triangle. Amongst these methods, Duval triangle method (DTM) is reported to be the most prominent. A new fault gas interpretation approach has been proposed in the present work. This method combines three Duval triangles with triangular membership functions (MFs) evaluated empirically for diagnosing the incipient faults. Like the existing Duval triangles, five gases, namely, hydrogen, methane, ethylene, ethane, and acetylene, are considered for the present study. Initially, the relevant gas percentages for the three Duval triangles are calculated and later converted into triangular fuzzy MFs. Finally, an expert rule-based method synthesizes the outcomes into a specific main fault type or subfault type. Test data of 139 transformers are used to compare the proposed method with the conventional DTM. The proposed approach is simple and can potentially determine the main faults and subfaults simultaneously based on numerical indices in a single fuzzy logic (FL) system. In addition, the proposed method has overcome the ambiguity in overlapping faults in the traditional methods.