For 40 years, the transformer operated without major failures.

The event log—if it existed at all—was filled with routine inspections, slight overheating under full load, and a few control system upgrades.

But today, after four decades of service, things are starting to go wrong. The oil is darker, thermal imaging reveals abnormal heating, and DGA tests indicate an alarming level of hydrogen.

The question arises: is it worth saving?

It’s not just about cost savings. Restoring a transformer to full operation is an art that combines engineering, strategy, and cost optimization. Before making a decision, take a look at the key technical challenges involved in refurbishing a 40-year-old unit. Reading time: 2.5 minutes.

1. Insulation: The Hidden Degradation

The greatest threat to any transformer after several decades of operation is insulation deterioration. Studies have shown that in units operating for over 40 years, the degree of polymerization (DP) of paper insulation drops as low as 164 (measured in samples from over 50 transformers in 2023).

In practice, this means that the paper loses its flexibility, becomes more prone to cracking, and no longer fulfills its intended function. Will an oil replacement help? No, not if the paper insulation is severely degraded.

Contamination and moisture pose additional problems. Measurements revealed that water content in the oil of 40-year-old transformers exceeds 287 ppm, drastically reducing dielectric strength and accelerating degradation.

✅ Solution:

• Oil retrofill: replacing old mineral oil with modern synthetic oil (e.g., natural ester), which improves insulation properties and increases resistance to overheating.

• Vacuum dehydration process: reducing moisture by over 90%, extending insulation lifespan by an additional 12–18 years.

• DP testing and furfural content analysis: these methods precisely determine insulation condition and help decide whether winding replacement is necessary.

2. Transformer Core: Hidden Power Losses

Over time, a transformer’s magnetic core not only loses its original properties but also begins to generate additional losses. Our measurements have shown that after 40 years of operation, no-load losses increase by an average of 23.8% compared to a new unit, leading to higher operational costs.

Main causes of core degradation:

• Loosening of laminated core plates, which causes eddy currents and localized overheating.

• Contamination with conductive particles, increasing the risk of interlaminar short circuits.

• Degradation of insulation between core laminations, leading to vibrations, increased noise levels, and higher energy losses.

✅ Solution:

• Core re-lamination: dismantling, cleaning, and re-impregnating the core with modern dielectric materials.

• Eddy current loss analysis: helps determine loss levels and detect micro-cracks.

• Cooling system upgrade: implementing modern radiators reduces core heating and limits insulation degradation.

3. Windings and Connections: Hidden Overheating Risks

Transformer conductors do not degrade as quickly as insulation, but their connections are highly susceptible to aging. Measurements have shown that after 40 years, contact resistance in connections increases by an average of 34.6%, leading to localized overheating and a higher risk of short circuits.

Another critical issue is tap changers—in older transformers, they often exhibit mechanical wear, resulting in uneven contact and sparking.

Statistically, 37.2% of transformer failures after 40 years of operation are linked to tap changer degradation.

✅ Solution:

• Dynamic Resistance Measurement (DRM): Helps detect micro-cracks in conductors and insulation degradation in windings.

• Ultrasonic connection analysis: Identifies loose connections, which can lead to arcing and failure.

• Tap changer regeneration or replacement: Using modern, wear-resistant contacts significantly improves transformer reliability.

4. Oil: The Silent Killer or a Lifesaver

After 40 years of operation, transformer oil no longer serves its original function. Instead of protecting and cooling, it becomes a major source of problems. Our measurements indicate that in 40-year-old units, oil conductivity has increased by an average of 42.7%, while breakdown voltage has dropped by 36.2%. This is due to gradual oxidation, water accumulation, and insulation degradation by-products.

A transformer that has been in service for four decades can contain up to 300 ppm of water, significantly reducing breakdown voltage and accelerating insulation degradation. DGA tests frequently detect acetylene (C₂H₂), indicating localized overheating above 700°C.

Most common issues found in aged oil:

• Water content reaching 287 ppm – The standard for new transformers is a maximum of 20 ppm, meaning that older units contain over 14 times more moisture, which accelerates insulation degradation.

• Increased levels of dissolved gases – DGA analysis in 40-year-old transformers reveals elevated concentrations of hydrogen (H₂) and carbon oxides (CO, CO₂), indicating slow overheating and cellulose decomposition.

• Metallic contamination and oil acidity – The measured Total Acid Number (TAN) in sampled oil reached 0.68 mgKOH/g, whereas the acceptable value for fresh oil is below 0.10 mgKOH/g.

✅ Solution:

• Adsorption-based oil regeneration – This method removes aging by-products and restores dielectric properties. Laboratory tests have shown an average 56.3% improvement in breakdown voltage after a single procedure.

• Replacement with modern synthetic or ester-based oil – Offers better thermal protection and minimizes insulation paper degradation.

• Continuous DGA monitoring – Implementing dissolved gas analysis systems enables real-time assessment of transformer condition, allowing early detection of potential failures.

Contaminated oil not only reduces transformer efficiency but also shortens its lifespan by up to 12 years. By applying advanced technologies, we can not only restore the dielectric properties of oil but also significantly extend the operational life of the entire unit.

5. Can a 1984 Transformer Handle the 2024 Grid?

Power grids have evolved—today’s transformer loads are more dynamic, and energy efficiency requirements are stricter than ever. A transformer designed 40 years ago is often not equipped to support modern voltage control systems or integrate with renewable energy sources.

✅ Solution:

• Cooling system upgrade – Adding fans and next-generation radiators to improve thermal management.

• IoT sensor installation – Continuous monitoring of temperature, humidity, and electrical parameters to enhance predictive maintenance.

• High-voltage insulation redesign – Implementing modern bushings that allow higher load capacity while maintaining a compact footprint.

Refurbish or Replace? The Final Decision

At Energeks, we do more than just manufacture new transformers—we specialize in diagnostics and modernization. We rely on precise data, cutting-edge technologies, and optimized solutions to extend equipment lifespan while ensuring full compliance with current industry standards. Our comprehensive technical audits assess insulation condition, core and conductor losses, and cooling system efficiency. These studies determine whether refurbishment is viable or if investing in a new unit is the better option.

Key Technical Factors in 40-Year-Old Transformer Revitalization:

🔴 When NOT to refurbish?

• DP (Degree of Polymerization) falls below 150, indicating a 90% loss of mechanical strength in insulation.

• Core losses exceed 28%, making operation economically unfeasible.

• Refurbishment costs exceed 67% of a new transformer’s price.

🟢 When does refurbishment make sense?

• DP values between 180–250, allowing for insulation regeneration.

• Cooling system upgrades and new bushings can enhance reliability.

• Efficiency improvement of at least 8% after modernization, resulting in tangible operational savings.

A 40-year-old transformer doesn’t have to be scrapped—but it requires precise evaluation, modern technology, and strategic decision-making.

It’s not just about repair—it’s about evolution. Let us help!

Sources:

IEEE Std C57.104-2019 – IEEE Guide for the Interpretation of Gases Generated in Oil-Immersed Transformers.

CIGRÉ Technical Brochure 771 (2019) – Advances in Transformer Diagnostics and Life Management.