Case study insulating oil: Extending service life of transformers

Deep-cleaning transformer oil instead of replacing it - this is the result of a collaboration between Tata Steel and Electrical Oil Services (EOS^®). Tata Steel, one of the leading steel manufacturers in Europe, was interested in how optimum maintenance of the insulation systems, in particular the insulation oil, could be integrated into the overall maintenance programme of its transformers. The objectives: to extend the service life of the transformers, avoid the replacement of transformers and save costs. Find out more about the scope, focus, planning and implementation of the EOS^® case study here. 

Scope of the case study: Condition analysis of several transformers in Port Talbot

In Port Talbot (Wales, UK), the focus was on 17 supply transformers from Tata Steel, each of which operates at 66 kV and supplies important parts of the steelworks. A complete replacement of the older transformers was out of the question for Tata Steel, but an alternative solution had to be found.   

The EOS^® engineers carried out a detailed analysis of each individual transformer. As part of this, a laboratory analysis (Transformer Condition Assessment, TCA) was also carried out for each of the 17 transformers in order to comprehensively assess the condition of the insulation system, in particular the oil quality and paper insulation.

Focus of the case study: The physical properties of the paper insulation and the results of the insulating oil tests 

EOS^® focused on the insulating oil test results and the physical properties of the paper insulation. The engineers recommended that Tata Steel perform a comprehensive deep cleaning (oil regeneration) of the entire insulating oil system of all the transformers analysed to extend their service life.  

Insulating oil regeneration offers important advantages over an oil change:

1. The entire insulating system is thoroughly cleaned, not just the insulating oil.   
2. The treatment is carried out without draining the oil, which minimises the risk of damage to the paper insulation.   
3. Option is available for the transformer to remain in operation during the entire process and only short interruptions are required for plugging and unplugging the connections.   
4. Significantly less contaminated transformer oil remains in the paper insulation compared to an oil change, as considerably more oil is cleaned during oil treatment.   
5. The process offers significant cost savings. Rather than completely changing the insulating oil or replacing the entire transformer, this method offers a much more economical option. It also extends the life of the transformer, which means that replacement can be avoided for a much longer period. 
6. Insulating oil regeneration harbours far fewer environmental risks. This is because there are not the same disposal risks as with an oil change by lorry. In addition, the lower number of lorry journeys helps to reduce CO₂ emissions and fossil resources are conserved.

Planning the case study: Developing a maintenance plan  

The initial aim was to develop a customised maintenance plan for on-site processing that takes into account the transformers themselves and not just the insulating oils.   

Which transformer first, which sequence makes sense? What logistical and time factors need to be considered? How long will how many Mobile Regeneration Units (MRU) from the EOS^® fleet be on site? The ideal sequence for the customer Tata Steel and the Port Talbot site was then worked out and set out in writing.    

In the following blog article you can find more information and guiding questions when planning an insulating oil regeneration:

• Minimise effort and costs: Mobile regeneration of transformer oil

Realisation of the case study: Serial treatment to achieve best deep cleaning results

Once the planning was complete, the transformer oil was regenerated step by step. In Port Talbot, the process began with the ST9 supply transformer, a 1959 transformer (10 MVA, 66 kV) with an oil volume of 17,000 litres.   

Mobile Regeneration Units (MRU) from EOS^® always consist of two specialised vehicles that are essential for the regeneration process. The first vehicle is equipped with devices for oil treatment (heating, filters, vacuum chambers), while the second vehicle contains columns with activated bauxite to adsorb impurities such as acids and sludge from the transformer oil. These impurities are caused by heat, oxygen and interaction with copper and iron during the oil ageing process. 

The serial treatment of the insulating oil in both systems ensures that the oil is left as good as new, which enables a higher proportion of deeply penetrated oil compared to a conventional oil change. The amount of acid removed is in direct proportion to time and temperature, with vibrations during regeneration having a supporting effect. Temperature control of the transformer core, optimally at around 70 °C, is crucial, but this increase can be limited by external temperatures and cooling factors.   

 
Read the complete Tata Steel case study including graphs and tables; published by the Transformer Magazine:  

• Tata Steel is using Electrical Oil Services' oil treatment process to extend transformer service life 

Result of the case study: Transformers remain powerful and stable for many years

The inhibitor content, which is measured annually, has not required topping up since the measure was taken. Electrical Oil Services engineers revisited the site and tested the insulating oil again.

Results after six years:

• colour value 1.0 and
• acid value was kept stable at 0.02 mg KOH/g.  

The work carried out by EOS^® on the ST9 demonstrates the clear benefits of transformer oil regeneration as part of a comprehensive programme to improve ‘transformer health’ and asset life extension. 

For Tata Steel, this insulating oil regeneration of the 17 important transformers means in concrete terms

• lower capital investment,   
• a better CO₂ balance and   
• better stewardship of well-built transformers that will be in service for many years to come. 

Read more:  

• Insulating oil recycler, lab expert, general contractor: Meet EOS^®!
• Insulating Oils & Services: Electrical Oil Services at a glance 

Conclusion: Extending the service life of transformers with an oil regeneration

The EOS^® case study at Tata Steel illustrates the benefits of transformer oil regeneration and its essential role in the sustainability and efficiency of transformer systems. The implementation of the EOS^® oil regeneration process not only extended the service life of the transformers, but also reduced operating costs and improved the environmental footprint. With increasing demands for energy efficiency and environmental responsibility, such solutions are important for companies to meet the challenges of the future. With this move, Tata Steel is setting a strong example for industry innovation and sustainable practices that benefit both the environment and the economy. 

Do you have any questions about the EOS^® Case Study or other topics relating to transformer oils? We look forward to hearing from you.