Transformer Oil Degassing: Methods, Principles, and Best Practices

Overview

Transformers are critical components of modern power systems, and their reliable operation is essential for power grid stability. Transformer oil plays a key role as an insulating and cooling medium in the transformer’s circulation system.

However, if transformer oil becomes contaminated with gas, moisture, or impurities, it can cause overheating, insulation breakdown, and even dangerous transformer failures. To prevent such risks, transformer oil degassing is a necessary maintenance process that removes dissolved and free gases from the oil, ensuring safe and stable operation.

Principles of Transformer Oil Degassing

Transformer oil degassing relies on physical and chemical principles to separate gas from the oil. By reducing pressure, applying heat, or using vacuum technology, gases are forced out of the oil and removed by external equipment.

The main transformer oil degassing methods include:

 1. Vacuum Oil Filling

 Process: Preheated oil is introduced into a vacuum tank. A vacuum pump removes gases from the tank, while the oil is injected into the transformer under pressure. Finally, the oil is circulated out, leaving the gases separated.

 Advantages: Effectively separates dissolved gases; suitable for small transformers.

 Limitations: Slow process, limited dehydration effect, and only moderate improvement in dielectric strength.

 2. Gas Cupping Method

 Process: By adjusting oil pressure, gases are forced into a separate chamber. A pressure differential then removes the extracted gases.

 Advantages: Faster than vacuum oil filling; suitable for smaller transformers.

 Limitations: Less thorough, may leave residual gases in the oil.

 3. Air Inhalation and Pressure Reduction Method

 Process: An adjustable suction pipe introduces controlled air inflow. By reducing pressure, dissolved gas in the oil escapes and is collected by auxiliary equipment.

 Advantages: Rapid and efficient gas removal; suitable for large transformers.

 Limitations: Requires precise control and specialized equipment.

 Choosing the Right Degassing Method

The best transformer oil degassing method depends on several factors:

 Transformer size

Small transformers → Vacuum oil filling or gas cupping.

Large transformers → Air inhalation and pressure reduction.

Operating environment → Humid or high-load environments require more efficient gas and moisture removal.

Oil quality → Testing is essential before degassing to determine contamination level.

Tip: For optimal results, combine oil quality testing with appropriate dehydration and degassing agents to improve both gas removal and insulation performance.

Conclusion

Transformer oil degassing is a vital step in transformer maintenance, helping to:

 Remove harmful gases and moisture.

 Improve insulation strength and cooling efficiency.

 Ensure safe and long-term operation of transformers.

By understanding the different degassing methods—vacuum oil filling, gas cupping, and air inhalation with pressure reduction—operators can ｓｅｌｅｃｔ the most suitable process for their transformer type and application.

Regular oil testing, combined with proper degassing, is the key to extending transformer life and preventing costly failures.