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.

A Computer Program for Fault Diagnosis and Assessment of Quality Insulation Oil in Power Transformer Based Dissolved Gas Analysis

“…IEC Basic Ratio Method is similar to the Roger's Ratio method except the ratio C 2 H 6 /CH 4 is excluded because of limited temperature range of decomposition see table 2. Other gas ratios such as C 2 H 2 /CH 4 , CH 4 /H 2 , C 2 H 4 /C 2 H 6 are used to generate the codes for interpretation [10]. Finally, the Roger's ratio method is regarded as the most widely used techniques.…”

Faults diagnosis and assessment of transformer insulation oil quality: intelligent methods based on dissolved gas analysis a-review

“…The main drawback of this study is that it only diagnoses the faults not assess the quality of transformer oil (Chromatography 2004). A computer program is developed by combining four DGA interpretation techniques to determine the fault condition of a transformer which gives more credence and accurate results to the predictability (Suleiman 2012) [12]. The four DGA techniques employ Rogers's ratio, IEC Basic ratio, Duval Triangle and Key Gas methods which are easy to use because the program performs multiple tasks in single run.…”

Enhanced condition monitoring of power transformers through improvement in accuracy of DGA interpretation

“…Hydrogen (H 2 ), Acetylene (C 2 H 2 ), Methane (CH 4 ), Ethane (C 2 H 6 ), Ethylene (C 2 H 4 ), Carbon monoxide (CO) and Carbon dioxide (CO 2 ): the concentration of these gases depends on fault type and severity [10]. Analyzing the concentration of the 7 key gases based on different DGA interpretation techniques such as Key Gas, Roger gas ratio, Doernenburg ratio, IEC gas ratio and Duval Triangle can indicate the fault type [11]. The accuracy of the applied interpretation techniques varies and can be dependent on personal experience [12], [13].…”