Condition Assessment of Power Transformers: Tools for Correlating Dissolved Gas Analysis and Off-Line Electrical Testing

Off-line electrical testing is a highly effective tool for evaluating the electromechanical and dielectric condition of power and distribution transformers. However, these tests require taking the transformer out of service, which is often undesirable. In practice, periodic analysis of oil samples, properly collected from the transformer, is commonly performed primarily Dissolved Gas Analysis (DGA). Oil samples are taken at regular intervals, and if a potential defect is detected, the transformer may be taken out of service either under fault conditions or as part of planned maintenance and off-line testing activities. This paper presents case studies with correlation (or lack thereof) between DGA results and off-line electrical test data. The combined use of both techniques enables a more comprehensive and accurate diagnosis, enhancing decision-making in predictive maintenance strategies.