【文章內(nèi)容簡介】 maintenance personals to increase the performance of transformer diagnosis. 2. DEVELOPMENT OF DIAGNOSIS AND INTERPRETATION Like many diagnostic problems, diagnosis of an oilimmersed power transformer is a skilled task. A transformer may function well externally with monitors, while some incipient deterioration may occur internally to cause a fatal problem in the latter development. According to a Japanese experience, nearly 80% of all faults result from incipient deteriorations. Therefore, faults should be identified and avoided at the earliest possible stage by some predictive maintenance technique. DGA is one of the most popular techniques for this problem. Fault gases in transformers are generally produced by oil degradation and other insulating materials, ., cellulose and paper. Theoretically, if an incipient or active fault is present, the individual dissolved gas concentration, gassing rate, total bustible gas (TCG) and cellulose degradation are all significantly increased. By using gas chromatography to analyze the gas dissolved in a transformer39。s insulating oil, it bees feasible to judge the incipient fault types. This study is concerned with the following representative bustible gases。 hydrogen(H2), methane(C2H 2), ethane(C2H6), ethylene(C2H4), acetylene(C2H2) and carbon monoxide(C0). Many interpretative methods based on DGA to diagnose the nature of incipient deterioration have been reported. Even under normal transformer operational conditions, some of these gases may be formed inside. Thus, it is necessary to build concentration norms from a sufficiently large sampling to assess the statistics. TPC investigated gas data from power transformers to construct its criteria. The developed knowledge base in this paper is partially based on these data. On the other hand, Dornerburg developed a method to judge different faults by rating pairs of concentrations of gases, ., CH /H , C H /C2H4, with approximately equal solubility and fusion coefficients. Rogers established mare prehensive ratio codes to interpret the thermal fault types with theoretical thermodynamic assessments. This gas ratio method was promising because it eliminated the effect of oil volume and simplified the choice of units. Moreover, it systematically classified the diagnosis expertise in a table form. Table 1 displays the ratio method as proposed by Rogers . The dissolved gas may vary with the nature and severity of different faults. By analyzing the energy density of faults, it39。s possible to distinguish three basic fault processes: overheating (pyrolysis), corona (partial discharge) and arcing discharge. Corona and arcing arise from electrical faults, while overheating is a thermal fault. Both types of faults m y lead to deterioration, while damage from overheating is typically less than that from electrical stress. Infect, different gas trends lead to different faulty types, the key gas method is identified.39。 For example large amounts of C H and H are produced with minor arcing fault 4. quantities of CH 2aid C2H4 2 may be a symptom of an arcing fault. 3. THE PROPOSED DIAGNOSTIC EXPERT SYSTEM This study is aimed at developing a rulebased expert system to perform transformer diagnosis similar to a human expert. The details of system processing are described below. The Proposed Diagnostic Method Diagnosis is a task that requires experience. It is unwise to determine an approach from only a few investigations. Therefore, this study uses the synthetic expertise method with the experienced procedure to assist the popular gas ratio method and plete practical performance. Experienced Diagnostic Procedure The overall procedure of routine maintenance for transformers is listed. The core of this procedure is based on the implementation of the DGA technique. The gas ratio method is the significant knowledge source. Some operational limitations of the gas ratio method exist. The ratio table is unable to cover all possible cases. Minimum levels of gases must be present. The solid insulation involving CO and CO are handled separately and the gas ratio codes have been developed mainly from a freebreathing transformer. Other diagnos