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Specialist Materials for Industry and Science



Midel offers both synthetic and natural esters (vegetable oil) for use with distribution transformers. MIDEL 7131 and MIDEL eN each provide different advantages under certain conditions, allowing you to choose the transformer oil that best suits your requirements.

Properties of Midel Esters

MIDEL 7131

Synthetic ester MIDEL 7131 has been specifically developed as a safe alternative to traditional fluid and dry-type distribution transformers, and has cultivated a strong reputation for high performance since it was introduced in 1978.

If your transformer is located outside in a climate where cold weather is likely, MIDEL 7131 is the best choice as it has a very low pour point, while it also performs perfectly well in warmer temperatures. Its superior oxidation resistance also makes it ideal for users with breathing equipment.


MIDEL eN is a natural ester (vegetable oil) produced from sustainable seed oil, making it a cost effective, environmentally friendly solution to many transformer oil requirements.

MIDEL eN, as with all natural esters, is suitable for sealed transformers, ideally in temperate or indoor locations.

Fire Safe Transformer Fluids

As distribution transformers are often located near or inside buildings, fire safety is a vital factor when choosing your transformer oil.

This is one of the key benefits of MIDEL 7131 and MIDEL eN, both of which possess a 100% fire safety record and have shown a K-class high fire point of greater than 300°C to IEC 61039.

Due to their superior fire properties MIDEL 7131 and MIDEL eN fluids are also listed as FM® Approved Less-Flammable Transformer Fluid. The use of an FM Approved Less Flammable Fluid represents a low fire hazard, can significantly reduce the extent of damage in a fire and can reduce installation costs. FM Approved liquid-filled transformers can be installed indoors. In addition, the products have gained the globally recognised UL® classification - EOUV dielectric medium and carry the UL Classified Mark, the widely trusted symbol for product safety and assurance.

What this means is that by using Midel esters in your distribution transformers, you greatly reduce the risk of fire and can consequently use less stringent protective measures.

Further Benefits of using Midel Esters for Distribution Transformers

High Performance

  • Greater moisture tolerance than mineral oil
  • Robust and stable, conducive to lower levels of maintenance
  • Low pour point

Greater Environmental Protection

  • Readily biodegradable according to OECD 301 and fully biodegradable according to IEC 61039
  • Non-toxic and non-water hazardous
  • MIDEL eN is a natural ester from a renewable source
  • Less threat to the environment than mineral oil

Excellent Customer Service

  • Multilingual commercial team
  • First rate customer care
  • Continued technical support from the transformer fluid experts

If you would like to know more about the best transformer fluids to use in your distribution transformers, you can contact us or consult our documents to find the information you need.

  • Apiezon
  • Metrosil
  • Midel
  • Wolfmet

Products of M&I Materials Ltd.