On-line DGA have the unique ability to continuously trend transformer fault gases and correlate them with other key parameters such as transformer load, oil and ambient temperatures as well as customer specified sensor inputs. This capability enables users to relate gassing to external events, a key to determine the existence or type of a fault. A study has also shown that some on-line DGA tools, offer better accuracy and repeatability than laboratory DGA. Specifically, those with on-board automated calibration verification that ensures performance to specification throughout the entire operating life of the monitor. This can improve the transformer asset manager’s decision timeliness and confidence when incipient faults are detected.
The ability to automatically populate traditional DGA diagnostic tools with on-line DGA data offers users of on-line DGA monitors unprecedented insight into the nature and identification of developing faults. The tools are typically ratio-based, and the on-line data set enables trending of fault gas ratios over time rather than the traditional static snapshots. Diagnostic outcomes can now be determined quickly and with more certainty than in the past. The use of on-line DGA monitoring has allowed the detection of developing faults in transformers on a timely manner. On-line DGA monitoring has produced multiple case studies that document the development of critical faults, which could cause catastrophic transformer failure if left undetected, in timeframes from a few days to a few weeks, where there was a low probability of capturing these rapidly developing fault conditions with a laboratory or portable-based transformer DGA testing program. This article presents some of those cases.