Transformers for the future

Midtfjellet Wind Farm is the largest of its kind in Norway and the very latest in wind turbine technology. It is also a testament to the excellence of Turkish transformer manufacturer BEST Transformer and their successful partnership with Nynas.

Case story

Best Transformer

  • CHALLENGE: Installing a complex transformer solution at Norway’s largest wind farm.
  • SOLUTION: Using NYTRO® 4000X with outstanding oxidation stability as the insulating oil.
  • RESULT: Low oil degradation and extended transformer life with minimum maintenance.


Since its founding in 1966, BEST Transformer has broken many records both locally and globally. The world-record products include the world's largest short-circuit tested auto-transformer (450 MVA) and the world's largest electric arc furnace transformer (315 MVA) with a 130 kA current flowing through its windings.

Balıkesir Electromechanical Industry Facilities (BEST) manufactures power, distribution, special, and dry-type transformers and exports to around 90 countries. In addition to high-quality transformers, the company produces all of the main components, such as tanks and cores, in-house.

“In 2023, we were the leading Turkish exporter in our sector, with a production capacity of 50,000 MVA,” notes Ahmet Kerem Köseoğlu, the company's Marketing & Communications Manager.

“Our focus on R&D allows us to design and develop the most challenging transformers. We can analyse and test transformers even before production starts, ensuring our products have a failure rate below the industry average.”

With a total production area of 170,000 sqm and seven test laboratories, BEST Transformer possesses strong design and production capabilities, supplying a variety of transformers and special solutions such as reactors, phase shifters, and mobile substations to their global customer base.

“Having control over the entire process, from raw materials to the end product, ensures our high quality,” says Ahmet Kerem Köseoğlu.

He anticipates continued strong growth in the future, driven by rising energy demand and the ongoing transition to electrification and renewable energy sources.

“The infrastructure of most grid operators is getting old, so grid renewal is going to increase transformer demand. To meet this demand, we are making significant investments in our manufacturing and test laboratories. We also offer carbon reduction options for transformers during the production and operation phases.”

One important project involving renewables is the Midtfjellet Wind Farm, which has been in operation since 2013. With 55 turbines, it is the largest of its kind in Norway. Positioning the turbines closely has resulted in clear economies of scale benefits in terms of infrastructure, operation and maintenance.

The wind farm currently has total capacity of 151 MW. The first 21 turbines were installed in 2011 along with a 130 MVA 300 kV transformer designed and manufactured by BEST Transformer. In the second phase, in 2013, another 23 turbines were installed alongside a 100 MVA unit.

At the time, Norway was planning to upgrade their High voltage (HV) grid from 300 kV to 420 kV, so they wanted the transformer to fit both voltages.

“Nynas visits us often to catch up on R&D projects or active tenders. They are always able to quickly check customer requirements and offer us the best solution.”

Ahmet Kerem Köseoglu, BEST Transformer.

“It was a challenging request. We decided to put an under-cover operation handle to switch between two operation modes. It was like designing two transformers for one unit,” says Ahmet Kerem Köseoğlu, who was a designer for the project. 

The customer requested NYTRO® 4000X as insulating oil in the transformers.

“Most likely because they knew it would resist oil degradation and provide oxidation stability, resulting in a longer transformer life and less maintenance.”

It was one of BEST Transformer’s first orders of NYTRO 4000X, so they researched the oil and discussed it with Nynas.

“It is always easy and fun to communicate with such an expert company. Sometimes, Nynas knows our customers even better than we do since they have been using Nynas solutions for a long time.”

The partnership between the two companies dates back many years. BEST has manufactured some 12,800 transformers with a total power of more than 128 GVA filled with Nynas insulating oils.

“We are lucky to have the Nynas Turkish office. It is easier when you have a local partner of a big brand like Nynas. They visit us often and catch up on R&D projects or active tenders and are always able to quickly check customer requirements and offer us the best solution, including project location delivery or port deliveries.”

As a designer in the early days of his career, Ahmet Kerem Köseoğlu learned a lot from the technical datasheets for Nynas’ products.

“They are well-organised and available in many languages. Nynas' technical documentation is a reliable source,” he notes, adding that the company invests in knowledge and R&D as much as BEST Transformer does.

“This gives us a very strong foundation. We see Nynas as our partner, more than just a supplier. We have a long-lasting relationship based on trust and mutual support, which we look forward to continuing for many years to come.”

All Transformer oils

Nynas has the world's widest range of transformer oils – developed to handle just about every conceivable climate, design and operating condition.

See a selection of our transformer oils based on their key characteristics, including viscosity. For more information on each product, simply download the relevant Product and Safety Data Sheets. See all products