When it comes to maintaining the health and efficiency of power transformers, choosing the right dissolved gas analyzer (DGA) is crucial.

These devices play a key role in monitoring the dissolved gases generated by transformer oil degradation, offering valuable insights into the internal condition of the transformer. With many online DGA systems available today, selecting the right one can be a daunting task.

The ideal analyzer should not only provide accurate and timely results but also be reliable, easy to integrate, and suited to the specific needs of your power system.

In this post, we’ll guide you through the key factors to consider when selecting an online DGA system, helping you make an informed decision that safeguards your equipment and enhances operational efficiency and an overview of current models available in the market.

Importance of Online Monitoring in Power Transformers

Traditionally, dissolved gas analysis was performed offline, requiring oil samples to be taken from the transformer and sent to a laboratory for analysis. While this method is effective, it has limitations due to its intermittent nature. By contrast, online monitoring provides real-time, continuous data on the concentration of dissolved gases. This proactive approach allows for early detection of faults, enabling utilities to act before they escalate into catastrophic failures.

Key advantages of online DGA monitoring include:

• Early fault detection: Allows utility operators to detect transformer issues (e.g., partial discharge, overheating, or arcing) as soon as they arise.
• Increased asset lifespan: Continuous monitoring leads to timely maintenance, reducing the risk of extensive damage and extending the transformer’s life.
• Enhanced reliability and safety: Prevents costly unplanned outages and improves the overall reliability of power networks.
• Cost efficiency: Although initial installation costs are be high, the long-term savings from avoiding breakdowns and reducing downtime outweigh these expenses.

Cost vs Benefit Motivation

The investment in online DGA systems comes with substantial upfront costs, including the purchase of the analyzer, installation, and integration into monitoring systems. However, the long-term benefits make the case for this investment. These benefits can be quantified through:

• Reduced downtime and unplanned outages: Preventing a single major transformer failure can save millions in equipment replacement and operational losses.
• Extended maintenance cycles: By identifying minor faults early, maintenance schedules can be optimized, reducing unnecessary maintenance and associated costs.
• Enhanced system planning: Real-time data from online monitoring enables operators to better plan asset management strategies, ensuring optimal transformer loading and usage.
• No Human intervention – No requirements for samples to be taken by people thus preventing errors in sampling and related contamination due to leaks and spillage of oil.

Although the cost of analyzers can be a deterrent for smaller utilities or plants, the financial return on investment (ROI) through increased operational efficiency, reduced downtime, and transformer longevity usually justifies the expense.

Criteria for Selecting a Dissolved Gas Analyzer

Choosing the right dissolved gas analyzer requires careful consideration of several key factors:

1. Number of gases detected: A good DGA system should measure key fault gases like hydrogen (H₂), methane (CH₄), ethane (C₂H₆), ethylene (C₂H₄), acetylene (C₂H₂), and carbon monoxide (CO).
2. Response time: For online systems, real-time or near-real-time monitoring is crucial. Faster response times allow for quicker corrective action.
3. Maintenance requirements: Consider the long-term maintenance needs of the device. Systems requiring frequent calibration or part replacements can increase operational costs.
4. Data integration: An ideal DGA analyzer should easily integrate with the utility’s supervisory control and data acquisition (SCADA) system for seamless data collection and analysis.
5. Cost and reliability: Evaluate the total cost of ownership, including installation, operational, and maintenance costs, as well as the system’s track record for reliability and longevity.
6. Environmental considerations: Systems should be rugged and able to perform well in diverse operating environments, including high temperature, humidity, and dust conditions.

Operating Criteria for Dissolved Gas Analyzers

DGA operates on the principle that certain fault conditions in transformers cause the degradation of insulating materials and oils, releasing gases that dissolve into the transformer oil. The analyzer samples this oil, detects these gases, and measures their concentration.

The two main types of detection are gas chromatograph-based analyzer which usually contains a carrier gas as a reference and routine calibration. The second type is an infra-red spectroscopy-based analyzer which usually do not require a carrier gas.

Generally, chromatography instruments are more accurate and have lower detections limits but the trade off is higher maintenance, calibration and consumables. Infra-red instruments generally have a simpler design, do not require carrier gas for calibration and tend to be lower capital cost however may compromise on accuracy and lower detection limits.

Compare current dissolved gas analyzers at this link.

Here are some critical operating criteria to ensure effectiveness:

• Detection thresholds: The analyzer must have sensitive sensors capable of detecting gases at low ppm levels to catch early signs of fault activity.
• Sampling frequency: In an online setup, sampling intervals should be short enough to provide near-real-time monitoring of gas buildup trends.
• Calibration and accuracy: Regular calibration is crucial to ensure the accuracy of readings, and analyzers should have the necessary internal mechanisms for this.
• Alarming and notification: The system should have configurable alarms that trigger when gas concentrations exceed predefined safe levels, allowing operators to take immediate action.
• Ease of Installation: It is important that the analyzers are installed correctly as this can affect the quality of sampling data.
• Training of Operators/Users – It is important that the user is properly trained on how to operate the analyzer, basic fault finding, alarms response, and interpretation of sample data.

Limitations of Dissolved Gas Analyzers

Despite their effectiveness, Dissolved Gas Analyzers are not without limitations:

• High upfront cost: The price of acquiring and installing online dissolved gas analysis system can be substantial, especially for smaller utilities or organizations.
• False positives/negatives: While advanced, DGA systems may sometimes report false alarms or miss emerging issues if gas levels change too slowly for detection.
• Complex interpretation: DGA results need to be interpreted by skilled personnel who understand the implications of gas levels and ratios. Anomalies could indicate several different types of faults, requiring further analysis to pinpoint the root cause.
• Environmental impact: Due to connections made directly to the main tank of the transformer, oil leaks and spills can result in contamination of the environment.

Current Analyzer Models in the Market

There are several manufacturers offering state-of-the-art DGA solutions for power transformers. Use this link to make high level comparison of the different models that are currently available.

Conclusion

Dissolved gas analyzers can play an indispensable role in maintaining the health and reliability of power transformers. While they require an initial investment, the long-term benefits, such as extended asset life, reduced downtime, and enhanced operational efficiency, make them a worthwhile investment. Careful selection of the right analyzer, with considerations for its detection capabilities, maintenance, and integration, is crucial. As technology continues to evolve, the future of transformer monitoring promises even more advanced and cost-effective solutions.

References

1. Sutton S, Skog J, Life Cycle Cost Analysis of Online Dissolved Gas Analysis Monitors, 25th International Conference on Electricity Distribution, Madrid, 3-6 June 2019
2. Nanfak, A., et al., Traditional fault diagnosis methods for mineral oil‐immersed power transformer based on dissolved gas analysis: past, present and future. IET Nanodielectr. 7(3), 97–130 (2024). https://doi.org/10.1049/nde2.12082