Dissolved gases in transformer oil can affect insulation performance and may indicate overheating, partial discharge, or other internal faults. Removing these gases helps maintain oil quality, but identifying their source is equally important.

For most transformer oil treatment applications, vacuum degassing is an effective method for removing dissolved gases from transformer oil. The appropriate treatment depends on the oil condition, gas concentration, and transformer operating requirements.

Why Does Transformer Oil Contain Dissolved Gases?

Dissolved gases can enter transformer oil through air exposure, oil handling, or chemical reactions inside the transformer during operation.

Common causes include:

• Overheating: Excessive thermal stress can generate gases as insulating oil and solid insulation materials deteriorate.

• Electrical discharge: Partial discharge and arcing can produce gases associated with electrical faults.

• Air contamination: Air may enter the oil during filling, maintenance, or handling.

Common gases monitored through dissolved gas analysis (DGA) include hydrogen, methane, ethylene, acetylene, carbon monoxide, and carbon dioxide. Their concentrations and patterns help engineers assess the condition of a transformer.

If DGA results indicate abnormal gas levels, investigate the potential cause before treating the oil. Vacuum degassing can remove dissolved gases, but it cannot repair an internal transformer fault.

How to Remove Dissolved Gases from Transformer Oil？

1. Use a Vacuum Transformer Oil Purifier

Vacuum degassing is widely used to remove dissolved gases from transformer oil. The process reduces pressure inside a vacuum chamber, encouraging dissolved gases to separate from the oil. A vacuum pump then extracts the released gases and vapors.

A typical vacuum transformer oil purification process includes the following steps:

• Oil heating: Controlled heating reduces viscosity and helps gases escape from the oil.

• Vacuum treatment: Oil enters a vacuum chamber, where reduced pressure promotes gas release.

• Gas extraction: A vacuum system removes the separated gases and vapors.

• Fine filtration: Filter elements remove solid contaminants such as dirt, fibers, and metallic particles.

• Oil discharge: The treated oil is returned to the transformer or storage tank according to the maintenance procedure.

Degassing performance depends on several factors, including vacuum level, oil temperature, flow rate, chamber design, and the time the oil spends under vacuum. Equipment selection should therefore be based on the required treatment results, not processing capacity alone.

2. Select the Right Transformer Oil Degassing Machine

A suitable transformer oil degassing machine should match the required treatment performance and actual operating conditions.

Consider the following factors when selecting equipment:

• Processing capacity: Choose a flow rate that meets the required treatment time and maintenance schedule.

• Vacuum performance: Confirm that the equipment can achieve the required residual gas level under specified operating conditions.

• Temperature control: Ensure that the heating system maintains an appropriate oil temperature without unnecessary thermal stress.

• Filtration accuracy: Select filter elements according to the required particle removal performance.

• Moisture removal: Determine whether vacuum dehydration is also required to reduce the water content of the oil.

A high-capacity machine is not automatically the best choice. The required gas removal performance, initial oil condition, and transformer maintenance requirements should guide equipment selection.

For large power transformers or applications with strict insulation requirements, it is particularly important to verify the expected treatment results with the equipment supplier.

What Is the Difference Between Degassing and Dehydration?

Degassing and dehydration are related processes, but they address different contaminants.

Degassing removes dissolved gases from transformer oil, while dehydration removes water. A properly designed vacuum transformer oil purifier can perform both processes during the same treatment cycle.

Mechanical filtration serves a different purpose: it removes solid particles such as dirt, fibers, and metallic debris. A conventional particle filter alone cannot effectively remove gases dissolved in oil.

The appropriate treatment depends on the actual oil condition. If the oil contains excessive moisture, dissolved gases, and solid particles, a combined purification process may be required.

How to Check Whether Transformer Oil Degassing Is Effective？

The effectiveness of transformer oil degassing should be verified through oil testing rather than estimated from processing time alone.

Depending on the application and maintenance requirements, evaluation may include:

• Dissolved gas analysis (DGA): Compare gas concentrations before and after treatment to assess changes in dissolved gas levels.

• Moisture content testing: Determine whether the water content has been reduced to the required level.

• Dielectric breakdown voltage testing: Evaluate the oil's dielectric performance as part of the overall oil condition assessment.

• Additional oil tests: Conduct other tests required by the transformer manufacturer or applicable maintenance standards.

The results should be interpreted according to the purpose of the treatment and the applicable acceptance criteria. Dielectric breakdown voltage alone cannot confirm that all dissolved gases have been adequately removed.

If abnormal fault gases reappear or continue to increase after treatment, further investigation may be necessary. Gas generation could continue inside the transformer even after the oil has been degassed.

Frequently Asked Questions

Can a regular oil filter remove dissolved gases?

No. A conventional particle filter removes solid contaminants. Dissolved gases generally require a suitable degassing process, such as vacuum treatment.

Does vacuum degassing also remove water from transformer oil?

Yes. A properly designed vacuum oil purifier can remove dissolved moisture as well as dissolved gases. Actual performance depends on equipment design, operating conditions, and the initial condition of the oil.

Can transformer oil degassing eliminate gases caused by an internal fault?

Degassing can reduce the concentration of gases dissolved in the oil, but it cannot eliminate the underlying cause of gas generation inside a transformer. If fault gases continue to increase after treatment, further investigation and DGA interpretation are necessary.

How often should transformer oil be degassed?

There is no universal treatment interval. The decision should be based on oil test results, transformer condition, maintenance requirements, and the cause of the gas contamination.

How do I choose a transformer oil degassing machine?

Consider the required processing capacity, target residual gas level, vacuum performance, moisture removal requirements, filtration needs, and site operating conditions. The supplier should clarify expected treatment performance under the specified conditions.

Conclusion

Removing dissolved gases from transformer oil helps maintain insulating oil quality and supports reliable transformer operation. Vacuum degassing is an effective treatment method when the equipment is properly selected and operated.

However, abnormal fault gases should never be treated as an oil quality issue alone. Dissolved gas analysis and transformer condition assessment are essential for determining whether the problem is related to contamination, normal ageing, or an internal fault.

Need a Transformer Oil Degassing Solution?

Sino-NSH provides transformer oil purification equipment designed to remove moisture, dissolved gases, and solid contaminants from insulating oil. Contact our technical team to discuss your oil condition, required processing capacity, and degassing requirements.