A DGA That Does More: Advanced Transformer Monitoring with the Serveron TM8
Dissolved gas analysis, or DGA, is a condition-assessment method used to identify gases generated inside oil-filled electrical equipment. Changes in gas concentrations and generation rates can provide evidence of developing thermal or electrical faults.
Online DGA monitoring automates this process, helping transformer owners track gas behavior over time instead of relying only on periodic oil samples. For critical transformers, frequent measurements can provide earlier visibility into changing conditions and support faster, more informed maintenance decisions.
Why transformer condition visibility matters
Power transformers remain essential to electricity generation, transmission, and distribution. At the same time, many operators are managing aging equipment, grid expansion, and the connection of new generation resources.
A 2024 U.S. Department of Energy report identifies the replacement of aging units, transmission expansion, and renewable-generation growth as primary drivers of large power transformer demand. The report reinforces the importance of maintaining the availability of transformers already in service, particularly because these critical assets can be difficult and time-consuming to replace.[¹]
This makes condition information increasingly valuable. Asset managers need to understand not only whether a transformer has an abnormal condition, but also whether that condition is stable, developing slowly or changing rapidly.
What is dissolved gas analysis?
Dissolved gas analysis examines gases present in transformer insulating oil. These gases may be generated when insulating oil or solid insulation is exposed to electrical or thermal stress.
Different gases and gas patterns can provide information about possible fault conditions. However, DGA should not be treated as a stand-alone verdict. Results must be interpreted alongside gas-generation rates, operating history, transformer loading, temperature, and other available condition information.
IEEE C57.104 provides guidance for evaluating gases generated in mineral-oil-immersed transformers.[²] IEC 60599 provides additional guidance for interpreting dissolved and free gases in mineral-oil-filled electrical equipment. IEC also emphasizes that DGA findings are guidance and that resulting actions require proper engineering judgment.[³]
Together, these standards establish DGA as an important part of transformer condition assessment while recognizing that meaningful interpretation requires more than a single measurement.
Laboratory DGA versus online DGA monitoring
Laboratory DGA and online DGA monitoring serve related but different roles.
| Consideration | Laboratory DGA | Online DGA monitoring |
|---|---|---|
| Data collection | An oil sample is collected and sent for analysis | Measurements are collected automatically at the transformer |
| View of condition | Provides results for a specific sampling point | Builds an ongoing trend over time |
| Measurement frequency | Determined by the oil-sampling schedule | Determined by the monitor’s configured analysis interval |
| Primary value | Detailed laboratory assessment | Visibility into changing gas concentrations and rates of change |
| Role in a DGA program | Supports confirmation and detailed investigation | Helps identify when conditions may require closer review |
CIGRE notes that online DGA monitoring can provide significant volumes of trend data, reveal high rates of change and help operators observe rapid deterioration in transformer condition. Online systems can also be configured to alert operators when measurements indicate developing conditions that may require prompt evaluation.[⁴]
Online monitoring does not eliminate the need for laboratory analysis or engineering review. Instead, it adds timely trend information that can help teams determine when closer investigation is needed.
Why monitor multiple gases?
A single-gas DGA monitor can provide a useful early indication that transformer conditions may be changing. A multi-gas monitor provides additional information that can help teams evaluate the possible nature of that change.
The Serveron® TM8™ On-Line DGA Monitor measures eight critical gases as standard:
- Hydrogen (H₂)
- Oxygen (O₂)
- Methane (CH₄)
- Carbon monoxide (CO)
- Carbon dioxide (CO₂)
- Ethylene (C₂H₄)
- Ethane (C₂H₆)
- Acetylene (C₂H₂)
Nitrogen (N₂) monitoring is also available upon customer request, giving the TM8 a nine-gas monitoring capability when required.
Because different transformer conditions can produce different gas patterns, measuring multiple gases provides more diagnostic context than monitoring a single gas alone. It also supports the use of established DGA interpretation methods for evaluating gas relationships and trends.
How does the TM8 measure dissolved gases?
The TM8 measures its eight standard gases through a single gas chromatography measurement system.
Gas chromatography is a well-established laboratory method for separating and measuring gases. By applying this method in an online monitor, the TM8 provides automated gas measurements at the transformer without requiring a new oil sample to be manually collected for every analysis.
The current TM8 specifications state that the system can perform DGA measurements on mineral and ester-based insulating fluids. However, the applicable interpretation method should always reflect the insulating fluid, transformer design and relevant industry guidance.
How frequently does the TM8 analyze transformer oil?
The TM8 supports user-selectable gas-analysis intervals from two to 12 hours, with four hours as the default setting.
When a configured rate-of-change alarm limit is exceeded, the monitor can automatically accelerate its analysis schedule. The default accelerated interval is one hour.
This change in frequency is important because an elevated gas level and a rapidly increasing gas level do not necessarily represent the same condition. More frequent analysis during a rate-of-change event gives operators additional data for evaluating how quickly the condition is developing.
Each measurement is date- and time-stamped, and up to approximately two years of data can be stored in the monitor’s memory.
Moving from gas measurements to diagnostic insight
Collecting gas measurements is only the first step. The data must also be visualized, compared and interpreted.
Serveron TM View™ provides tools for transformer-monitor management, data visualization and DGA analysis. Its capabilities include gas-in-oil trend charts, multiple Duval Triangle analyses, Rogers Ratios, Basic Gas Ratios, and gas-level and rate-of-change alarms.
These tools allow teams to examine gas behavior through more than one diagnostic approach. Comparing results from different methods can contribute to a more complete assessment, but final conclusions should still consider transformer design, service history and operating conditions.
Looking beyond dissolved gases
Changes in dissolved gases can be more meaningful when operators can compare them with what was happening to the transformer at the same time.
In addition to its gas measurements, the TM8 can monitor or correlate information such as moisture-in-oil, oil temperature, ambient temperature and transformer load. Moisture-in-oil and oil-temperature monitoring are available as options. Transformer-load information can also be added using the available load-monitoring option.
This additional context can help engineers evaluate whether gas generation increased during a period of higher loading, whether moisture or oil temperature changed at the same time, and whether the gas trend continued after operating conditions returned to normal.
The monitor does not make the final engineering decision. It provides more of the information required to investigate changing transformer conditions.
Bringing transformer condition data together
For larger monitoring deployments, SmartSUB® extends the analysis beyond an individual DGA monitor.
SmartSUB includes the DGA analysis capabilities of TM View and can combine TM8 data with information from other transformer condition-monitoring devices. These can include tank pressure, cooling-bank current, winding current and temperature, bushing monitoring and partial discharge monitoring.
Bringing this information together can help asset managers evaluate transformer condition more broadly instead of reviewing each monitoring system separately.
This is where an advanced DGA program becomes more than gas collection. It becomes part of a connected condition-monitoring strategy that relates DGA findings to the transformer’s electrical and thermal operating environment.
Supporting centralized access to DGA data
The TM8 supports several communication interfaces and industrial protocols for remote data access.
Standard interfaces identified in the current TM8 brochure include RS-232, RS-485, fiber Ethernet, and an internal POTS modem. Optional interfaces include cellular and copper Ethernet.
Supported protocols include TCP/IP, DNP3, Modbus RTU, ASCII, OPC, and IEC 61850. These communication options help organizations make DGA information available to the appropriate teams, depending on the site and existing communication infrastructure.
Where is advanced online DGA monitoring most valuable?
The level of monitoring required should reflect the transformer’s importance, operating environment, condition and potential consequences of failure.
The TM8 brochure identifies generator step-up transformers, large transmission transformers, and critical substation transformers as key applications. It can also support important generation, transmission, and distribution power transformers where frequent condition information is required.
Advanced multi-gas monitoring may be particularly relevant when operators need frequent measurements, multiple diagnostic methods and greater visibility into changing gas conditions. It may also be appropriate as part of a broader transformer-monitoring strategy, particularly when data must be accessed remotely or combined with other condition-monitoring information
Turning DGA data into better maintenance decisions
Online DGA monitoring does not replace laboratory testing, engineering judgment or a complete transformer maintenance program. Its value comes from giving asset teams frequent, repeatable measurements that show how transformer conditions are changing over time.
The Serveron TM8 provides eight-gas online DGA as standard, with nitrogen monitoring available upon customer request for a total of nine measured gases. It combines gas chromatography, adjustable analysis intervals, diagnostic tools and additional transformer condition data in one monitoring solution.
When connected with TM View or SmartSUB, this information can become part of a broader transformer condition-assessment process.
For operators responsible for critical transformers, the question is no longer only whether DGA should be performed. It is whether the available DGA data is frequent, detailed and connected enough to support decisions when transformer conditions begin to change.
Explore the Serveron TM8 On-Line DGA Monitor
References
- U.S. Department of Energy, Large Power Transformer Resilience Report, 2024:
https://www.energy.gov/sites/default/files/2024-10/EXEC-2022-001242%20-%20Large%20Power%20Transformer%20Resilience%20Report%20signed%20by%20Secretary%20Granholm%20on%207-10-24.pdf - IEEE, IEEE C57.104-2019: Guide for the Interpretation of Gases Generated in Mineral Oil-Immersed Transformers:
https://ieeexplore.ieee.org/document/8890040 - International Electrotechnical Commission, IEC 60599:2022 – Guidance on the Interpretation of Dissolved and Free Gases Analysis:
https://webstore.iec.ch/en/publication/66491 - CIGRE, Guideline for Online Dissolved Gas Analysis Monitoring:
https://www.cigre.org/userfiles/files/News/2022/TOR-JWG%20A2_D1_67_Guideline%20for%20online%20dissolved%20gas%20analysis%20monitoring.pdf - Qualitrol, Serveron TM8 Multi-Gas On-Line Dissolved Gas Monitor:
https://www.qualitrolcorp.com/products/TM8
