Improving accuracy of DGA interpreation of oil-filled power transformers needed for effective condition monitoring

Abstract

The probability of equipment failure increases over time as the age and rate of use increases. Since faults are the major cause of these failures, there are several ways and means used towards predicting fault occurrence and thus preventing the equipment from failing by diagnosing its condition. In oil filled transformers, the Dissolve Gas Analysis (DGA) is used as one of the well-established techniques to predict incipient faults inside its enclosure. With the existence of more than 6 known methods of DGA fault interpretation techniques; there is the likelihood that they may give different conditions for the same sample. Using a combination of many of the diagnostic methods will therefore increase the accuracy of the interpretation and so increase the certainty of the transformer condition. This paper presents a computer program based condition diagnosis system developed to combine four DGA assessment techniques; Rogers Ratio Method, IEC Basic Ratio Method, Duval Triangle method and Key Gas Method. A user friendly GUI presented to give a visual display of the four techniques and the output of the combined interpretation. The result of the prediction analyses done to test the accuracy of the program shows an overall DGA prediction accuracy of 97.03% compared to the 91% of the most reliable individual method; Duval Triangle and near elimination of ‘no prediction’ condition.