Filling transformers with oil:
Ecol at Baltic Power

The height of the turbines will exceed 200 metres and the rotor envelope area of each turbine will be approximately 43.000 m².

Construction of the wind farm began in 2024 and it is scheduled to be operational in 2026. Baltic Power has the opportunity to play a key role in Poland’s energy transition, contributing to domestic energy security while helping to combat air pollution. ​

why power transformers are needed at Baltic Power?

Power transformers enable transmission of the electricity output by the wind turbines into the onshore power grid. Wind turbines generate an output voltage lower than required for efficient long-distance transmission.

The electricity output first goes to an offshore substation, where transformers step up the voltage (usually to 220-275 kV) to minimise transmission losses. The stepped-up voltage is output via underwater cables to an onshore substation, where its transformers readjust the voltage again, this time to a level required for export to the domestic transmission grid.

how transformers allow transmission of electrical power from sea to land:

step 1: Energy production
Wind turbines generate low-voltage electricity, which is insufficient for transmission over long distances.

step 2: Voltage increase – offshore power station
Transformers increase the voltage (up to 220–275 kV), which minimises losses during transmission.

step 3: Transmission via submarine cables
The energy is transmitted via a high-voltage submarine cable to a station on land.

step 4: Voltage adjustment – onshore power station
Transformers adjust the voltage to a level compatible with the national power grid.

step 5: Distribution to recipients
The energy enters the transmission grid, from where it is distributed to end users.

the role of transformer oil

Transformer oil is mission-critical to power transformers. It provides effective electrical insulation of the windings while dissipating the heat generated while the transformer is online.

By virtue of its properties, the oil penetrates and fills all inner voids in the transformer for protection against external factors and prevention of partial discharge. This application demands routine inspection of transformer oil quality and performance; it is fundamental to the reliability, efficiency, and maximum service life of power transformers.
 

what is the procedure for transformer oil filling?

The process of filling a power transformer with dielectric oil depends on many factors, especially the transformer unit type, power rating, and application. Parameters like oil quality, vacuum level, oil temperature, filling rate and ambient conditions must conform with the manufacturer’s guidelines and prevailing technical standards. For this reason, each transformer oil filling operation requires strict compliance to applicable procedures and the use of appropriate equipment.

the key steps of filling a power transformer with dielectric oil include:

• 1. Assessment of the power transformer’s condition – prior to filling with oil, the transformer is thoroughly inspected for damage and leaks.
• 2. Vacuum system preparation – setting up the valves, connecting the vacuum generating plumbing, and monitoring instruments.
• 3. Vacuum buildup – the sufficient vacuum level is generated and held according to the specifications of the transformer. This step is done to make all water turn from liquid to gas and evacuate it from the power transformer.
• 4. Oil preparation – the oil is purified and its water content removed prior to filling the transformer (these operations can be done by e.g. active thermal processing or vacuum processing), along with testing the key parameters of the oil (like breakdown voltage, water content, and acid number).
• 5. Installing the fittings – the transformer is prepared for filling with oil by installing the required connections and safety equipment. Once the installation process is complete, the power transformer is isolated and passes a pressure test to verify the pressure integrity of all connections prior to the next steps.
• 6. Dry air protection – after the installation process and only if the pressure test is a pass, the transformer interior is protected by pumping dry air (or nitrogen gas). This prevents condensation and protects the insulation materials from absorbing moisture. The air dehumidification system is an integral part of the equipment in the transformer service container, which also houses the dielectric oil.
• 7. Vacuum filling with oil – this process is done at a preset vacuum pressure to ensure the removal of all gasses from the transformer, minimising the risk of partial discharge. A key factor in accurately filling a transformer with oil is the correct filling rate, which allows the internal materials (e.g. insulation paper) to fully and evenly absorb the oil.
• 8. Pressure equalisation with dry air or nitrogen gas and oil treatment – once the transformer has been filled, the system is stabilised and additional filtration of the oil in the transformer tank is run to remove residual gases and impurities.
• 9. Sampling and quality control – a post-process oil analysis allows verification of its conformity to the specifications.
• 10. System bleeding – the last step is to vent all gases from the transformer, followed by final oil sampling for verification system.

Ecol at Baltic Power

our task: Filling transformers with oil

Our company played an important role in the Baltic Power project, supporting the construction of its onshore transformer substation. Our project task was the delivery and priming eight high-power transformers of the substation with dielectric oil. Each was filled with carefully prepared oil, which was delivered in tankers and processed before and during the filling operation. In total, we processed more than 766,000 litres of oil, maintaining full control over the quality of each charge, which was crucial for the subsequent safe commissioning of the transformers.

The process uses a transformer oil treatment unit which removes water, gases and solids from mineral-based transformer oil, as well as natural or synthetic esters.

The process is crucial to ensure the safe and efficient operation of power transmission equipment. Water and gases dissolved in the dielectric oil can significantly impair its properties and ultimately deteriorate the operating safety of power transformers.

The filling process included oil take-off from the tankers, preliminary lab testing, dehydration and degassing, and vacuum pumping into transformer tanks.

At each stage, our company out detailed tests on the quality of the oil, from its delivery to the final physical and chemical testing (using dissolved gas analysis, DGA).

equipment used

The task was completed using a high-performance oil treatment unit, Ekofluid FILOIL 12000 designed for servicing large power transformers. The FILOIL 12000 removes water, gases and solids from the oil, improving its dielectric and cooling performance. The oil treatment unit can operate on both online and offline transformers; it is fully automated thanks to a PLC and integration with a SCADA system.

The oil treatment process involves heating the oil indirectly, which eliminates the risk of local overheating, followed by filtration to 0.5 micrometres, and finally, degassing and dehydration in a vacuum chamber. The unit’s system uses vane and Roots pumps with coalescent filters to ensure high performance of dissolved gas and water separation.

Additional vacuum valves and thermal protection safeguard the unit and personnel, while automatic oil flow control allows the operating parameters to be precisely matched to operational conditions. This advanced technology ensures efficient and safe preprocessing of the oil before it is fed to the transformers.

transformer oil diagnostics

Integral to the whole process was the enhanced transformer oil diagnostics carried out at each stage of the task. We performed pre-testing after oil delivery on site, an analysis during oil treatment and final testing after filling the transformers.

The key tests were the determination of water content, breakdown voltage testing, and DGA (dissolved gas analysis) chromatography that facilitate verification of the technical health of the power transformer before recommissioning.

With this comprehensive diagnostic approach, we were assured that the oil met the highest quality standards and that the transformers were ready for continued operation in a safe and trouble-free manner.y.

the result

Despite many technical challenges, the task was a complete success. Thanks to the use of dedicated equipment, rigorous quality control and the experience of our team, we were able to successfully fill eight high-power block transformers with dielectric oil that met all the requirements specified in the manufacturer’s standards and recommendations.

During the project, dozens of laboratory tests were performed to confirm the relevant physical and chemical parameters of the oil, including its purity, breakdown voltage, water content and dissolved gas concentrations (by DGA).

Thanks to careful organisation and the use of modern oil treatment methods, the filled transformer systems were ready for the safe application of live voltage, a key step in preparing the infrastructure for one of the largest energy projects in recent years.

technical highlights

→ Correct protection of the environment and the working area: deployment of containment trays

As part of the work carried out at the Baltic Power project site, our company used dedicated containment trays, which are critical to worksite protection that involves tanks with transformer oil. Containment trays minimise the risk of oil spills and facilitate immediate response in such an emergency.

The solution was implemented with the utmost attention to personnel safety and environmental protection, in accordance with the prevailing health and safety regulations and in-house design standards. This practical and effective safety feature was highlighted as an example of good practice in Baltic Power’s monthly health and safety newsletter.

→ sample laboratory test report

Below is a specimen of a dielectric oil test report from the Ecol laboratory. It features key physical, chemical and diagnostic parameters to assess the health of the oil and the equipment in which the oil is used.

This type of report is an important tool to support decision-making processes in maintenance, service planning and failure prevention.

Click the image to see the details in full resolution:

what’s next for Baltic Power?

The Baltic Power project, jointly developed by ORLEN and Northland Power, is confidently entering the next stages of construction. In May 2025, Poland’s first operations and maintenance base for offshore wind farms was officially opened in the town ow Łeba. The base, equipped with a quay and cranes, a high-rise warehouse and technical backend, will support the operation of the wind farm for approximately 30 years.

At sea, installation work is underway that now features the assembly of tower base adapters for the wind turbines. In July, the first successful installation of a 15 MW offshore wind turbine was completed (a total of 76 turbines will be installed).

In parallel, onshore in the municipality of Choczewo, the fit-out of the power substation with key components, such as 300 MVA transformers, continues. The wind farm is scheduled for completion in 2026, after which it will begin operation, providing clean electrical power to more than 1.5 million households.

Work progress updates are available at: https://balticpower.pl/#aktualnosci

summary

Baltic Power will be one of the world’s first wind farms using 15 MW turbines, which will generate around 4,000 GWh of electricity annually, reducing CO₂ emissions by around 2.8 million tonnes. This project represents a significant step towards Poland’s energy transition and strengthens the country’s position in the renewable energy sector.

We are proud to be part of this groundbreaking project and to support Poland’s energy transition. While being a technological challenge for our company, working on the construction of one of the first offshore wind farms in the country brings us great satisfaction in making a real contribution to the growth of renewable energy sources.