Practical experience of dissolved gas in transformer oil for the detection of incipient faults

Abstract

Although the association between dissolved gas analysis (DGA) in transformer oil and incipient faults is well established, interpretations for this association are not. There are different approaches to the interpretation of DGA results, some standards use individual gas limits while others use key gases or ratios (such as Rogers). Different with numerous publications on the subject presented about DGA interpretation techniques that are available for the detection of incipient faults, this paper has addressed how we meet the challenges in real cases and introduce experience learnt in implementing DGA diagnostic approaches to look after each fault-specific transformer. Some key learning points are (1) when properly applied, DGA signature is powerful for detecting a wide range of incipient faults in transformers and assisting in determination when to remove the transformer from service for repair or replacement; (2) Knowledge of transformer design strength and weakness together with information of historic operation and maintenance enable the results of DGA to be interpreted correctly; and (3) Utilizing these practical experience allow the user to manage the risk of failure and discount the need for replacement.