Optical Filter Set for On-line and Real-time Dissolved
Gas Analysis of Transformer Oils

Author: Reto Keller, Business Development Manager at Materion Balzers Optics, Balzers, Liechtenstein

Dissolved Gas Analysis (DGA) is a pivotal technique in the realm of transformer diagnostics, offering a window into the internal health and functioning of power transformers. This analytical method involves the examination of gases present in the insulating oil of transformers, providing crucial insights into potential faults and abnormalities. As electrical equipment ages or undergoes stress, electrochemical processes can lead to the generation of specific gases, known as fault gases, which are indicative of degradation inside the transformer.

The significance of DGA lies in its ability to detect and identify these fault gases, enabling early detection of incipient faults such as overheating, partial discharges, and insulation degradation. By monitoring changes in gas concentrations over time, engineers and maintenance professionals can assess the condition of the transformer and make informed decisions regarding maintenance or replacement, thereby enhancing the reliability and longevity of the transformer.

Failure Modes and Detection Possibilities in Transformers
Analyzing the concentrations and ratios of the fault gases allows experts to identify specific failure modes.

Here are some common failure modes associated with specific gases:

1. Methane (CH₄) and Ethane (C2H₆): Indicate low-energy electrical discharges, such as corona discharges, and are associated with partial discharge activity.
2. Ethylene (C2H₄): Signals high-energy discharges, typically from overheating or arcing, suggesting severe insulation or overheating issues.
3. Acetylene (C2H₂): Presence of acetylene points to severe faults like arcing and is indicative of high-temperature conditions, such as the presence of hot spots or insulation breakdown.
4. Hydrogen (H₂): Suggest overheating, often associated with localized hot spots or excessive electrical loading.
5. Carbon Monoxide (CO) and Carbon Dioxide (CO₂): Indicate thermal degradation of cellulose insulation, providing insight into the aging of the transformer.

Advantages of On-Line Monitoring versus On-Site Sample Extraction
The traditional method of DGA involves periodically extracting insulating oil samples from a power transformer and analyzing them in a laboratory using techniques like gas chromatography. The results of these tests may prompt a more detailed visual inspection and/or replacement of the oil.

However, this approach is reactive and time-consuming. In contrast, online monitoring systems continuously track dissolved gas levels, providing real-time insights into transformer health. This proactive method reduces the need for frequent on-site interventions, as issues can be identified promptly. Online monitoring streamlines maintenance efforts, minimizes downtime, and ultimately enhances the efficiency of transformer diagnostics.