| Company | Vattenfall |
| Location | Berlin, Germany |
| Date | 1992 to present |
| Project Overview | Vattenfall retrofilled 6/10kV, 400–600 kVA distribution transformers in Berlin with Midel 7131 to improve performance, safety, and reliability. |
| Products | MIDEL 7131 synthetic ester fluid |
Overview
In Berlin, keeping the power network running safely comes with unique environmental challenges. Large parts of the city are classified as water protection areas, where strict rules apply to prevent contamination.
Vattenfall, one of Europe’s major utility companies, needed a safer way to operate its distribution transformers in these sensitive zones. MIDEL 7131, a synthetic ester fluid, became a key part of that solution.
Challenge
Traditional transformers use mineral oil, which can pose a risk if leaks or spills occur—especially in water protection areas.
For Vattenfall, this meant finding a way to reduce environmental risk without replacing large numbers of existing transformers. Any solution also needed to maintain performance over time, even in transformers exposed to the environment.
Solution
In 1992, Vattenfall launched a pilot project to test retrofilling—replacing mineral oil with MIDEL 7131 in existing transformers.
The process was thorough. Transformer windings were removed, cleaned with MIDEL 7131, and dried in an oven before being reinstalled. The units were then refilled with the synthetic ester fluid.
This approach reduced the remaining mineral oil content to less than 3%, meeting strict environmental standards in Germany.
Benefits
Using MIDEL 7131 significantly reduced the environmental risk associated with transformer operation in sensitive areas.
The fluid also showed strong technical performance, maintaining insulation strength and managing moisture effectively—even in free-breathing transformers exposed to air.
This allowed Vattenfall to upgrade existing assets instead of replacing them, saving time and cost while improving safety.
Results
Over a 13-year monitoring period, the retrofilled transformers continued to perform reliably. The fluid maintained its key properties, confirming the long-term success of the approach.
Based on these results, Vattenfall expanded the program, retrofilling around 350 transformers and installing new units using MIDEL 7131.
Today, around 2,500 synthetic ester-filled transformers are operating across the network, helping deliver reliable power while protecting the environment.