Most Common Gases Detected by a Dissolved Gas Analyser

A Dissolved Gas Analyser (DGA) is critical in evaluating the health and performance of oil-filled electrical equipment, particularly transformers. It detects dissolved gases in transformer oil, which might indicate probable flaws and degradation in the equipment. By analyzing the type and concentration of these gases, a Dissolved Gas Analyser can provide early warning signs of malfunctions, allowing for preventive maintenance before serious issues occur.

This article will explore the common gases detected by a Dissolved Gas Analyser and what their presence may indicate in terms of transformer health.

Types of  Gases Detected By a Dissolved Gas Analyser

1. Hydrogen (H₂)

A Dissolved Gas Analyser can measure hydrogen, which is one of the most significant gases. It is a key indicator of a variety of transformer faults. The presence of hydrogen in transformer oil is typically associated with electrical discharges, such as partial discharge (low energy electrical fault) or arcing (high-energy electrical fault). Both of these conditions can lead to insulation breakdown, equipment damage, or even catastrophic failure.

• Partial Discharge: This is a low-energy electrical phenomenon caused by localized insulation degradation. The Dissolved Gas Analyser picks up the production of hydrogen, even in small amounts, which serves as an early warning signal of potential issues.

• Arcing: A more severe condition, arcing generates higher concentrations of hydrogen and is indicative of a serious fault in the transformer. Immediate investigation and action are required to prevent major damage.

2. Oxygen (O₂)

Oxygen is another critical gas detected by a Dissolved Gas Analyser. While transformers are designed to operate in an oxygen-free environment, leaks or poor sealing can introduce oxygen into the system, leading to degradation of the transformer oil and insulation.

• Oil Oxidation: The presence of oxygen accelerates oil oxidation, which can result in sludge formation and a decrease in insulation quality. If oxygen levels increase, it is important to check the transformer for leaks or breaches in the seal system.

3. Carbon Monoxide (CO)

Carbon monoxide is an important gas for monitoring the condition of the transformer’s solid insulation materials, particularly cellulose. The Dissolved Gas Analyser identifies the presence of carbon monoxide when the cellulose insulation undergoes thermal degradation.

• Cellulose Decomposition: As the paper insulation in transformers ages or is exposed to excessive heat, it breaks down, producing carbon monoxide. This gas acts as a reliable indicator of aging insulation, especially when detected alongside carbon dioxide.

4. Carbon Dioxide (CO₂)

Alongside carbon monoxide, carbon dioxide is another key gas that the Dissolved Gas Analyser detects when transformer insulation materials are degrading. It reveals information on the transformer's solid insulation's long-term condition.

• Aging of Paper Insulation: When the Dissolved Gas Analyser detects both carbon dioxide and carbon monoxide, it typically suggests that the transformer’s paper insulation is breaking down. High levels of carbon dioxide can also indicate thermal stress, especially if the gas is present in combination with others, like ethylene.

5. Methane (CH₄)

Methane is another gas that a Dissolved Gas Analyser frequently detects. Its presence is often associated with thermal faults within the transformer, such as hot spots caused by overheating. Methane is produced when the oil or solid insulation overheats and starts to break down.

• Low Temperature Overheating: When the transformer is mildly heated, methane is created in relatively small proportions. This may indicate localized insulation or oil overheating, often due to poor cooling or excessive load.

• High Temperature Overheating: In cases of significant overheating, methane levels will increase dramatically, indicating serious thermal stress on the transformer that requires prompt attention.

6.  Ethylene (C₂H₄)

Ethylene is considered a crucial gas when assessing thermal faults, particularly those involving higher temperatures. A Dissolved Gas Analyser often detects this gas when there is significant thermal stress inside the transformer.

• High-Temperature Faults: Ethylene is mainly generated when the oil is exposed to high temperatures. When a Dissolved Gas Analyser detects increasing levels of ethylene, it usually points to overheating of the transformer oil and insulation system.

• Cellulose Decomposition: Ethylene is also produced during the decomposition of cellulose-based insulation materials, which is a serious concern. This can eventually lead to irreversible transformer damage if not addressed.

7. Acetylene (C₂H₂)

Acetylene is among the most harmful gases discovered by a Dissolved Gas Analyser. This is clear evidence of arcing within the transformer.. Unlike partial discharge, arcing involves high-energy electrical discharges, which can cause severe damage.

• Electrical Arcing: The generation of acetylene is a clear sign of electrical arcing, which typically results in extreme heating and potentially catastrophic failure. When a Dissolved Gas Analyser detects acetylene, immediate action is necessary to prevent severe damage or fire.

• Arcing in Oil: Acetylene is produced when oil comes into contact with electrical arcs. If acetylene is detected, it is typically a red flag for technicians, signaling that urgent maintenance or repairs are needed.

8. Ethane (C₂H₆)

Ethane is a gas commonly produced during thermal degradation processes within a transformer. The presence of ethane, as detected by a Dissolved Gas Analyser, often indicates a mid-range thermal fault or localized overheating of the transformer oil.

• Thermal Faults: Ethane is typically produced in moderate amounts when transformer oil undergoes decomposition due to moderate heating. If ethane is detected at higher concentrations, it can be a sign of more serious thermal stress, particularly when combined with other gases like ethylene.

Read More, Dissolved Gas Analyser: Precise Monitoring for Equipment

Conclusion

A Dissolved Gas Analyser is an essential tool for detecting early signs of faults within transformers. By monitoring gases such as hydrogen, methane, ethylene, acetylene, ethane, carbon monoxide, carbon dioxide, and oxygen, this tool helps in diagnosing potential issues before they become critical. Regular analysis and timely intervention based on these gas readings can extend the life of transformers, reduce maintenance costs, and prevent catastrophic failures.