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Specialist Materials for Industry and Science

Fluid Filled Transformers

Fluid Filled Transformers

Transformers using Midel ester-based oils have been shown to perform significantly higher than those filled with standard mineral oil. While mineral oils were for many years the product of choice in transformers, in recent years studies have revealed how ester-based fluids offer a far superior alternative.

Whereas mineral oil is highly flammable, MIDEL 7131 and MIDEL eN have been shown to provide a 100% fire safety rating. Mineral oils also contain corrosive sulphur and are potentially damaging to the environment.

Midel esters can also be proved to increase the life expectancy of fluid filled transformers with their greater moisture tolerance. Our synthetic and natural transformer oils are discussed in more detail below:

MIDEL 7131

Our synthetic ester is the ideal choice for a broad range of applications, and works just as well in sealed or breathing transformers. High risk environments such as offshore or underground transformers require a safe, environmentally friendly fluid, and MIDEL 7131 can provide this.

It boasts a high fire point of 300°C, while its 100% fire safety record provides the necessary protection for areas where an outbreak of fire could have disastrous consequences. MIDEL 7131 is non-corrosive and offers a low maintenance transformer fluid solution, with its increased reliability and safety setting it apart from mineral oil alternatives.


Our natural dielectric oil MIDEL eN provides another high performance alternative for fluid filled transformers, and this environmentally friendly transformer oil is made using renewable materials.

This is proved by its outstanding biodegradability and is non-corrosive, which will help to minimise the environmental impact should a spillage occur. It is also enjoys a similarly high standard of fire safety to that provided by MIDEL 7131.

It is important to note that MIDEL eN performs most efficiently when used in sealed transformers, and so is perfect for applications when distribution transformers are located in built up areas or indoors.

For more information on either of our esters, you can contact us or have a look around our documents section.

  • Apiezon
  • Metrosil
  • Midel
  • Wolfmet

Products of M&I Materials Ltd.