Used oil disposal: What type of used transformer oil does EOS® accept?

When a transformer is serviced or decommissioned, one thing is almost always left behind: used insulating oil. For operators, this raises a crucial question: What should be done with the used transformer oil – and who will take it? This is where Electrical Oil Services comes in. The insulating-oil specialist and certified waste management company accepts transformer oils in almost any condition, analyses their quality, and ensures their safe disposal or – where possible – regeneration for reuse.  

As insulating oil in transformers ages, many questions arise: Where should the used transformer oil go? Does it need to be disposed of? Can it still be reused? And who is authorised to collect it? Electrical Oil Services (EOS^®) supports transformer operators precisely at this stage – providing analysis, collection, disposal or regeneration to ensure the safe and compliant handling of used transformer oil.  

What kind of used transformer oil does Electrical Oil Services accept? 

Electrical Oil Services operates dedicated production facilities in Germany (Duisburg) and the UK (Stanlow), each with specific capabilities for processing and handling used transformer oils. Across these sites, EOS^® accepts a wide range of spent oils, whether removed from operating equipment, reserve tanks or during maintenance work.

Used transformer oils includes:

• Non-chlorinated insulating and heat-transfer oils based on mineral oil 
  
• Synthetic insulating and heat-transfer oils, for example based on ester or silicone 
  
• Other insulating and heat-transfer oils, such as special blends or older stock oils 
  
• Naphthenic transformer oils, which are particularly well suited to regeneration 
  
• Aged or contaminated transformer oils, even with PCB content up to 20 ppm in Duisburg and up to 50 ppm in Stanlow

The Duisburg facility primarily accepts oils that can be recycled into high-quality base oils, while Stanlow processes and regenerates transformer oils.  

Stanlow can accept all the oils listed. However, EOS^® main objective is to recover oils that can be returned to the circular process; where recycling is not feasible (for example with certain synthetic oils), we can still assist by arranging compliant disposal through trusted specialist partners.

Whatever the condition of the oil, getting in touch with Electrical Oil Services is always worthwhile. Each batch of used transformer oil is individually assessed, and EOS^® always finds the right solution – from professional regeneration or recovery to referral to specialised partners where, for example, a high PCB concentration prevents in-house treatment.

This ensures that operators’ used transformer oils are handled safely, in full compliance with regulations, and as efficiently as possible.  

First step: Every used insulating oil is individually tested 

It is crucial to determine whether the used transformer oil can still be regenerated or must be disposed of as oil waste. To make this assessment, the following key parameters can be measured:

• Water content 
  
• Acidity (neutralisation number) 
  
• Breakdown voltage 
  
• PCB concentration 
  
• Metals 
  
• Level of solid contaminants

Testing scopes may vary between facilities: at Stanlow, used oil is primarily tested for PCB content, metals and solid contaminants, while more detailed laboratory analysis (e.g. for water content, acidity and breakdown voltage) is carried out at other EOS^® locations.  

Second step: Decison on what to happen to the collected used transformer oil 

Only after the analysis of the used transformer oil can the next step be decided. Based on the laboratory results, transformer operators receive a clear recommendation on what should happen to their used transformer oil – and which option is the most economical.

1. Recyclable transformer oil:
If the insulating oil meets the required quality, it can be regenerated within the EOS^® Closed Loop Model. Through cleaning, degassing and processing, the oil is restored to the specifications of a high-grade insulating oil. The result is EOS^® Premium, a proven transformer oil that meets IEC 60296:2020 Type B and is reused in many installations.

2. Non-recyclable transformer oil:
If the oil is heavily contaminated or contains too much PCB, EOS^® refers operators to approved specialists who can carry out proper disposal in accordance with local legal requirements

Read more in this interview:

• EOS waste management company - Dispose of or save used transformer oil?

Why can’t every used transformer oil be recycled and reused? 

Transformer oils age at different rates – depending on factors such as load, temperature, exposure to air or contamination by metals and cellulose fibres. Some used oils are so heavily oxidised that regeneration is no longer practical. PCB contamination is also an issue. 

Process: From transformer oil removal to re-use 

The services provided by Electrical Oil Services cover the entire life cycle of insulating oil – from filling, continuous analysis, regeneration or removal, through laboratory testing and classification, to its return to service:

1. On-site oil removal or delivery:
Whether the insulating oil is removed directly by EOS^® from the transformer or delivered by the operator – both options are possible.

2. Oil sampling and laboratory analysis:
Every sample of used transformer oil is tested in our laboratory for its electrical, chemical and physical properties.

3. Collection and transport of oil:
EOS^® is a certified waste management company and ensures that every batch of used transformer oil is handled safely, transparently and in full compliance with legal standards.

4. Oil regeneration or disposal: Suitable transformer oils are processed either in EOS^® mobile units or recycling facilities.  

5. Return and refilling of transformer oil:
For on-site projects, EOS^® can refill new or regenerated insulating oil directly after draining.

This structured approach allows customers to rely on Electrical Oil Services as a full service provider for transformer oil and maintenance work. As a company, we ensure complete transparency and traceability – every step is documented and every oil sample clearly identified.

Read more:

• Insulating oil recycler, laboratory expert, general contractor: Meet EOS^®!
• Case study insulating oil: Extending service life of transformers
• Electrical Oil Services presents: The EOS^® Closed Loop Model 

Conclusion: EOS has the right solution for every type of used transformer oil 

Electrical Oil Services turns what is often seen as a regulatory obligation into a transparent and reliable process. The company provides cost-efficient, compliant and sustainable solutions for the renewal, treatment or disposal of transformer oil – from the initial analysis through to full documentation. 

• No effort for operators:
  EOS^® takes care of analysis, transport and treatment of used oil, or arranges safe disposal through trusted partners in cases of high PCB contamination. 
  
  
• Resource, not waste:
  Used transformer oil remains part of the circular process wherever possible – helping to save costs and protect the environment. 
  
  
• When disposal is required: As a certified waste management company, EOS^® ensures proper treatment and provides all legally required documentation. 

Get in touch with the experts at Electrical Oil Services if your transformers require oil servicing or used-oil management – we provide tailored advice, professional support and the right solution for every installation. 

Do you have any questions? We will be happy to answer them.