Can the condition of transformer oil be improved without taking the transformer out of service?
In some cases, yes. Transformer oil can be treated or refined while the transformer is in operation using treatment systems designed to operate with the transformer in service. The oil continuously passes through the treatment system and returns to the transformer after specific contaminants have been removed.
However, choosing this method is not based solely on the desire to reduce downtime. It starts with the oil condition, test results, and transformer operating conditions.
What Can Be Treated During Operation?
The treatment capabilities vary depending on the system used, but Online Oil Treatment may primarily target:
- Moisture.
- Particles and solid contaminants.
- Dissolved gases.
- Certain oil degradation products, depending on the treatment technology.
IEC 60422:2024 indicates that insulating oil treatment may include processes such as filtration, moisture removal, and degassing. It also addresses Reconditioning and Reclaiming processes depending on the type of treatment and the extent of oil deterioration.
Why Can Online Treatment Be a Practical Option?
For transformers that are critical to the production process, shutting down the transformer for oil treatment may not be operationally practical.
Online treatment can improve certain oil properties without waiting for a scheduled shutdown, provided that the transformer condition and treatment system allow this approach.
Industrial technologies are available to remove moisture and particles from transformer oil while the transformer remains energized and in service, with the treatment process monitored during operation.
Does Every Decrease in Oil Quality Require Treatment?
Not necessarily.
The decision should start with oil analysis, rather than relying only on the oil's appearance or age. Moisture and particles, for example, can affect the oil's ability to withstand electrical stress, while other indicators may point to oxidation or oil deterioration.
Good practice therefore relies on comparing test results against the relevant condition limits and standards for the equipment. IEC 60422 provides guidance on monitoring, assessing, and determining appropriate treatment for mineral insulating oils in service.
At Triple M, we recommend starting the oil treatment decision with test results and transformer condition assessment, rather than relying solely on a decrease in oil quality.
What Role Does Oil Analysis Play in the Decision?
Oil treatment should not be considered separately from transformer condition assessment.
For example, DGA – Dissolved Gas Analysis can provide indications of thermal or electrical activity inside the transformer. IEC 60599:2022 provides guidance on the interpretation of dissolved and free gas analysis for assessing the condition of oil-filled electrical equipment and supporting decisions on further actions, while results must be interpreted within the engineering context of the equipment.
Therefore, if the problem is related to ongoing internal deterioration or continuous thermal or electrical activity, oil treatment alone will not address the root cause.
How Is the Treatment Result Evaluated?
The important step is not simply operating the treatment unit, but verifying its effect on the oil.
Test results can be compared before and after treatment, including:
- Breakdown Voltage (BDV)
- Moisture Content
- Acidity
- Interfacial Tension (IFT)
- Dielectric Dissipation Factor / Tan Delta
- DGA, when included in the transformer condition assessment program
This comparison helps determine whether the treatment achieved an actual improvement or whether a different intervention is required.
In transformer oil treatment activities, Triple M follows an approach that links oil analysis results with the condition of the equipment to determine whether treatment is appropriate or whether a different maintenance intervention is required.
When Is Online Treatment Not the Right Solution?
If the results indicate severe oil deterioration or a type of contamination that cannot be addressed by the available filtration and treatment process, oil replacement or more extensive maintenance may be the more appropriate option.
Similarly, indications of an internal fault do not mean that improving the oil properties will solve the problem. In such cases, the underlying cause must be addressed, while oil analysis remains part of the overall transformer condition assessment.
Online transformer oil treatment is not simply a way to avoid shutting down a transformer; it is a technical decision based on oil condition, test results, and the nature of the problem.
When the condition is treatable, Online Oil Treatment can help restore certain oil properties, reduce the need to handle large quantities of oil outside the transformer, and allow the equipment to remain in service.
When the data indicates severe deterioration or an internal fault, oil treatment should be considered as part of a broader maintenance strategy—not as a substitute for addressing the underlying problem.
We emphasize that effective treatment starts with proper diagnosis; the objective is not simply to improve oil properties, but to select the appropriate intervention based on transformer condition and technical data.
Sources
- IEC 60422:2024 — Mineral insulating oils in electrical equipment – Supervision and maintenance guidance.
- IEC 60599:2022 — Mineral oil-filled electrical equipment in service – Guidance on the interpretation of dissolved and free gases analysis.
- IEC 60296:2020 — Fluids for electrotechnical applications – Mineral insulating oils for electrical equipment.
- Maschinenfabrik Reinhausen — Oil Processing / Online Transformer Drying.