Vegetable oil-filled transformer

Innovation in the ultra-high voltage range

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Vegetable oil for a sustainable energy supply

Transformers use high-quality mineral oil as an insulating fluid and as a coolant. However, vegetable oil also has the required insulating properties. As a renewable, carbon-neutral and biodegradable resource, vegetable oil has environmental benefits and a lower fire load.

In addition, there are also benefits associated with the use of vegetable oil-filled transformers in water reserves. Since vegetable oil is a natural, biodegradable resource that is not hazardous to waters, these transformers can also easily be used in water reserves and flood plains. Transformers using mineral oil, in contrast, must fulfil very stringent special building restrictions. Another benefit of vegetable oil-filled transformers: due to the vegetable oil's high fire point they can also be installed in areas with extended fire regulations, for example in residential areas.

Transformers with vegetable oil-based insulation are becoming increasingly significant. This technology marks an important step towards future-proofing the grid infrastructure. At present, the technology is still at the research and development stage. However, the long-term objective is to roll it out widely.

Full power at all voltage levels

Transformers are the key elements of all substations. They are used to transform voltages to different levels. Long-range transport of electricity takes place at the ultra-high voltage level, since losses are at a minimum and efficiency is at its highest at this level. The transformer reduces the voltage to a lower level so that it can be fed into the local distribution grid. Depending on the required capacity, consumers are connected to 220kV or 380kV ultra-high voltage, 110 kV high voltage or medium / low voltage (below 50 kV).

Mineral oil – vegetable oil

Conventional oil transformers contain mineral oil that is used as a coolant and insulation medium. It is very resistant to heat and stress. Transformers filled with mineral oil are smaller and lighter than vegetable oil transformers. Vegetable oil has the same function in the transformer as mineral oil. However, it is biologically degradable and has a very high flash point, so it is even safer than mineral oil. This simplifies the installation of the vegetable oil transformer in the substation and increases the number of location options.

Benefits of vegetable oil

The flash point of the vegetable oil is very different from that of the mineral oil. While vegetable oil doesn’t combust until it reaches 360°C, mineral oil combusts at 170°C. There is also a big contrast between the biological degradability of the two cooling and insulation oils. The vegetable oil is 100% biologically degradable, whereas the mineral oil hardly degrades at all.

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Building the energy supply of the future

Thinking ahead and developing innovative solutions is key in order to ensure a secure transmission system. The new transformer installed by TransnetBW at its Bruchsal-Kändelweg substation, the first one in the ultra-high voltage range operating with vegetable oil, marks an important step towards a sustainable future for the energy industry.

The long-term objective is to make the use of vegetable oil-based insulating fluid profitable enough for general use, not just for water conservation and special fire protection areas. TransnetBW uses this pilot project to explore how conventional substances such as mineral oil can eventually be substituted.

Around 96 tons of vegetable oil are contained within the transformer.

The vegetable oil-filled transformer commissioned in 2014 has already delivered important insights in terms of durability, cooling performance, mechanical performance and lubricating properties. The transformer will continue to help in developing the solutions of the future. Current research is looking into how vegetable oils from different plants can be mixed, for example.

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