| It is a widely used and quit efficient method to use gas dissolved in oil as character to diagnose transformer fault. This article has deeply analyzed the principle of using gas dissolved in oil as character to diagnose transformer fault, and analyzed the three ratio method to diagnose power transformer which is currently widely used. Three-ratio method has high exactness rate, but it may bring about errors or mistakes if the ratio is just at the boundary of the coding-zone. This is the unavoidable fault of valve diagnosis.This article has researched on the Three-ratio method fuzzy coding diagnosis focusing on the problem, finding that although it fuzzy the boundary of coding-zone, it has still the valve problem and can't solve it perfectly.A new diagnosis model-fuzzy synthesis diagnosis was developed in thisarticle. With the actual condition of transformer, this article has mentioned how to calculate the vector C, to set the relation matrix R, and to select fuzzy calculation factor.This work is a part of "transformer condition monitoring" of condition monitoring center in Hunan Electric Power Test & Research Institute, its goal is to establish a suitable expert diagnosis system. Considering the actual condition, deeply research on the design of knowledge base, consequence-unit, the structure of database and the principle and realization of fuzzy expert diagnosis system has researched.Based on fuzzy synthesis judgement diagnosis model, this article has developed a set of transformers fault diagnosis fuzzy expert system base on the platform of Windows2000 with Visual C++ 6.0 as kit.According to history data and actual faults, this article has tested this model, Proving that this model can develop the advantage of Three-ratio method, make up the shortage of Three-ratio method, increase the exactness rate of diagnosis. At the same time this system has many good characteristics such as the friend interface, easy operation and maintenance, calculating fast and accurate and so on..
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