Diagnosis of Power Transformer Faults based on Five Fuzzy Ratio Method

Dissolved Gas Analysis is one of the most useful method to detect incipient faults in transformer. Amongst the conventional DGA methods, IEC three ratio method is widely used. One of the disadvantages in its present form is that a significant number of DGA results inservice fall outside the existing IEC codes and cannot be diagnosed. To overcome this limitation, additional eighteen new combinations to the existing nine are proposed in this paper. Further, Ratio codes are quantized to define the crisp boundaries of 0,1 and 2. In practice these boundaries are non crisp (Fuzzy) especially under multiple faults condition. These codes could lead to errors in diagnosis moving across the crisp boundaries from one fault to another. To overcome these limitations, Five Fuzzy ratio method for diagnosis of multiple faults is developed. The paper used 100 different cases to test the accuracy of these methods in interpreting the transformer condition. Key-words: Expert System (ES),Dissolved Gas Analysis(DGA),International Electro Commission Method (IEC), Incipient Faults, Power Transformer, Fault Diagnosis, Fuzzy Diagnostic System, Ratio Methods.