English

Abstract

Dissolved Gas Analysis (DGA) (1-4) of insulation oil in an oil insulated transformer is one of the most useful techniques for the detection of the incipient faults. The various methods, such as Gas key method, Ratios method, Graphical representation method are well known to interpret DGA results. When more than one fault exists in a transformer, these methods sometimes fail to diagnose. 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. 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. MATLAB based scripts prove that the proposed method can overcome the drawbacks of the Conventional Three Ratio Method that cannot diagnose multi-fault and no matching codes for diagnosis. In this paper a Fuzzy Logic based approach which can diagnose multiple faults is presented.