Diagnosis of power transformer faults on fuzzy three-ratio method

Dissolved gas-in-oil analysis (DGA) is one of the most useful methods to detect transformer incipient faults. Among the diverse conventional DGA methods, IEC three-ratio method is widely used, but in many cases this method can not accurately diagnose(such as no matching, multiple faults). This paper proposes a fuzzy three-ratio method; it is considered that the drawbacks of the conventional three-ratio method lie in: when the ratio crosses the coding boundary, codes change sharply, but in reality the boundary should be fuzzied. Based on this assumption, this paper first propose the fuzzy membership functions for codes "zero", "one", "two", then it transfer the conventional logic "AND" and "OR" used in IEC three-ratio method into fuzzy logic and put forward the diagnosing steps of this method. Simulation proves the proposed method can overcome the drawbacks of the conventional three-ratio method that can not diagnose multi-fault and no matching codes for diagnosis, thus, it greatly enhanced diagnosing accuracy