Insulating oil takes on several key functions in transformers: it insulates electrical components, dissipates heat and reliably protects the unit during operation. Yet the choice is wide-ranging – from conventional mineral oils to synthetic esters and recycled options. Read on to find out which insulating oils are available, what their strengths and limitations are, and how companies can make the right decision for their application.
Insulating oils at a glance: Which insulating oil is the right choice?
Every insulating oil has its justification – the key is to match the properties with the specific requirements of the installation. In addition to technical factors, international standards such as IEC 60296:2020 should always be considered to ensure quality and reliability.
Economic efficiency and resource conservation are equally important, as the choice of the right insulating oil affects not only operational performance but also long-term costs and a company’s sustainability balance.
1. Mineral insulating oils
Mineral insulating oil is the most widely used worldwide. It is derived from crude oil and processed to meet the required electrical and thermal properties.
- Advantages: good insulating characteristics, efficient heat dissipation, globally available, cost-effective, easily recyclable
- Disadvantages: flammable, potentially harmful to the environment and groundwater in case of leaks
Despite these well-known drawbacks, mineral oil remains a proven solution for many operators, as infrastructure, recycling processes and availability are geared towards this oil.
2. Synthetic esters for transformers
Synthetic esters are increasingly used as an alternative to mineral oils, particularly in urban areas or installations with strict fire safety requirements. Their chemical structure gives them greater resistance to oxidation and ageing.
- Advantages: biodegradable, high flash points, reduced fire risk, good ageing stability
- Disadvantages: more expensive than mineral oil, less established in large-scale applications
In densely populated regions or critical infrastructure, synthetic esters provide a safety advantage that can justify the higher costs.
3. Silicone insulating oils
Silicone oils are specialised products used where conventional insulating oils reach their limits. This includes transformers operating at very high temperatures or under extreme environmental conditions.
- Advantages: non-flammable, very high thermal stability, long service life
- Disadvantages: significantly higher costs, more difficult to dispose of, rarely available as standard
Their use therefore remains limited to niche applications – but for operators with specific safety requirements, they can represent the most suitable solution.
4. Natural esters (bio-based insulating oils)
Bio-oils are produced from renewable raw materials such as rapeseed, soya or sunflower oil. They are considered particularly sustainable as they help to reduce the ecological footprint. In practice, they are gaining importance due to their high level of biological degradability.
- Advantages: environmentally friendly, non-toxic, high flash points, biodegradable
- Disadvantages: higher viscosity (reduced cooling performance), more expensive than mineral oil, recycling still difficult at present
In pilot projects and in companies with a strong sustainability focus, bio-based insulating oils are regarded as a forward-looking option. However, their widespread use will depend on the future development of efficient recycling processes.
5. Recycled insulating oils
Recycled or regenerated oils form a bridge between efficiency and sustainability. Modern processes allow used mineral insulating oils to be reconditioned so that they meet the properties of new products.
- Advantages: resource-saving, cost-efficient, CO₂ reduction by avoiding new production, compatible with existing transformers
- Disadvantages: quality depends heavily on the reconditioning process – compliance with IEC 60296:2020 is essential
This makes recycled insulating oils an equivalent alternative to new mineral oils – without compromising technical performance. The reuse of insulating oil therefore offers a practical solution for companies wishing to ensure operational reliability while at the same time achieving their sustainability goals.
More infos on recycled transformer oil:
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Consider product variety and sustainable options in insulating oils
A comprehensive view of insulating oils shows that there is no universal solution, but rather a range of different options that can be appropriate depending on operating conditions and objectives.
Suppliers on the market therefore provide various products – from new mineral insulating oils and synthetic esters to recycled variants. Of particular importance are those approaches that combine operational reliability with resource conservation and economic efficiency.
Electrical Oil Services (EOS) is one of the leading suppliers in Europe and also follows this approach offering a broad portfolio of transformer oils – from new mineral insulating oils to expertly recycled premium grades.
Read more:
Further information on recycled oils can be found in this article:
Conclusion: Choosing insulating oil requires balancing technology, cost and sustainability
Insulating oils are indispensable for the safe and efficient operation of transformers.
While mineral oils have traditionally accounted for the largest share, recycled insulating oils today offer an equal alternative – technically equivalent and environmentally sound. Synthetic esters and bio-oils broaden the options, particularly where environmental or safety aspects are prioritised, while silicone oils cover specialised applications.
For operators this means: The choice of the right insulating oil should always be based on the operating conditions, the relevant standards, as well as on technology, economic efficiency and sustainability.
2 extra tips:
Go directly to the product page of our recycled insulating oil:
Learn more about insulating oil recycling from a cost perspective:
