Dissolved Gas Analysis (DGA) is one of the most valuable diagnostic tools available for evaluating the condition of oil-filled transformers. By measuring gases dissolved in the insulating fluid, DGA can help identify developing thermal and electrical conditions before they lead to more serious equipment problems.
However, collecting DGA data is only part of the process. Proper interpretation requires looking at the complete picture—including gas patterns, historical trends, transformer operating conditions, and sample quality.
Here are five common DGA mistakes transformer owners and maintenance teams should avoid.
1. Looking at Individual Gas Concentrations in Isolation
One of the most common mistakes when reviewing DGA results is focusing too heavily on a single gas concentration.
Different transformer conditions can generate multiple gases, and the relationship between those gases often provides more useful diagnostic information than one concentration alone. An elevated gas may be significant, but it should be evaluated as part of the transformer’s overall gassing pattern.
Looking at the complete gas profile can help determine whether the results are consistent with conditions such as overheating, partial discharge, arcing, or insulation degradation.
The takeaway: Evaluate the overall DGA pattern rather than making maintenance decisions based on a single gas.
2. Ignoring Gas-Generation Rates and Historical Trends
A single DGA result provides a snapshot of transformer condition at a particular point in time. While that snapshot is useful, comparing results over time can provide much greater insight.
Tracking the rate at which gases are being generated can help determine whether a potential fault is stable, slowly progressing, or developing rapidly. For example, an elevated gas concentration that has remained relatively unchanged may warrant a different response than a concentration that has increased significantly in a short period.
Routine DGA testing and consistent historical records make it easier to identify meaningful changes and prioritize maintenance appropriately.
The takeaway: Don’t just ask, “How high are the gases?” Also ask, “How quickly are they changing?”
3. Using Diagnostic Methods Without Considering Operating Conditions
Diagnostic tools and guidelines, including IEEE guidance, Key Gas Analysis, and methods such as the Duval Triangle, can provide valuable insight into transformer condition. However, they should not be interpreted without considering the transformer’s operating history and conditions.
Factors that may influence DGA results include:
- Transformer loading
- Operating and oil temperatures
- Insulating fluid type
- Recent maintenance or operating events
- Sampling techniques
- Transformer design and service history
Understanding what was happening with the transformer before and during the sampling period can provide important context for interpreting the results.
The takeaway: DGA interpretation should combine established diagnostic methods with knowledge of the transformer’s actual operating conditions.
4. Treating Every Abnormal Result as an Immediate Transformer Failure
An abnormal or flagged DGA result deserves attention, but it does not automatically mean a transformer is approaching imminent failure.
High gas concentrations can indicate abnormal conditions, but determining the severity and urgency requires additional context. Historical trends, gas-generation rates, operating conditions, electrical testing, and visual inspections may all help determine what is actually occurring within the transformer.
Before making major maintenance or operational decisions based on an abnormal DGA result, the finding should be evaluated alongside the other available transformer condition data.
The takeaway: An abnormal DGA result is a reason to investigate, not automatically a reason to assume failure is imminent.
5. Neglecting Sampling and Laboratory Quality
Even expert DGA interpretation depends on the quality of the sample being analyzed.
Improper sampling techniques can introduce air, contamination, or other variables that may affect the accuracy of laboratory results. Using the correct sampling containers, following proper procedures, carefully handling samples, and avoiding excessive delays before sending samples to the laboratory are all important parts of obtaining reliable DGA data.
Laboratory quality is equally important. Consistent testing procedures, appropriate quality controls, and experienced interpretation help turn a properly collected oil sample into useful information about transformer condition.
The takeaway: Reliable DGA diagnostics begin before the sample ever reaches the laboratory.
Getting More Value From DGA Testing
Dissolved Gas Analysis is most valuable when it is treated as part of an ongoing transformer condition-monitoring strategy rather than as a single pass-or-fail test.
Combining quality sampling and laboratory analysis with historical trending, operating information, and other transformer condition data provides a more complete understanding of asset health. This approach can help maintenance teams identify developing conditions, determine when additional investigation may be necessary, and make more informed maintenance decisions.
At MVA, our transformer oil diagnostics team provides DGA testing and expert analysis to help customers better understand what their results may be indicating and how transformer condition is changing over time.
Need DGA testing or a routine transformer oil testing program? Request a customized transformer oil testing quote based on your transformer testing needs today.