Diagnosis of Power Transformer Condition using Dissolved Gas Analysis Technique: Case Studies at Geothermal Power Plants In Indonesia

For many years, to determine the type of inceptive failure on power transformers, practitioners often use the Dissolved Gas Analysis (DGA) to obtain conclusions about the causes of failures. To determine the failure that occurs in the transformer, the generation of certain gases within a transformer is an incredible indicator that has been proven so far. Because of the sensitivity and accuracy in measuring gases, this technique has become standard practice in normal maintenance activities at electric utility companies. This article presents the investigation of dissolved gas analysis (DGA) of four generator step-up (GSU) transformers at geothermal power plants in Indonesia. Each transformer insulating oil data were collected during yearly routine inspection and the DGA measurements at power plants for the duration of 6 years was obtained. DGA measurement result was analyzed and processed using the dissolved gas analysis method based on IEEE C57-104 and IEC 60599 standards. The interpretation of measurement data is conducted using four methods, that is key gas, gas ratio, Duval Triangle, and The Four Gases. Rogers Ratio, Doernenburg Ratio and Gas Ratio Combination are the gas ratio methods used in this study. The results of the diagnosis of generator step-up (GSU) transformers using DGA analysis showed that all four transformers were in different conditions for each analysis method. This paper highlights the importance of keeping track of DGA history and using several DGA interpretation methods to add confidence to the result.