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MIDEL 7131 is the world’s leading biodegradable synthetic ester transformer fluid.

MIDEL 7131 is used in power and distribution transformers, both sealed and free-breathing, to provide fire safety, environmental protection, and cost savings. It is also utilized in various demanding sectors such as Renewable Energy, Traction, Mining, Marine, Underground, and for Retrofilling.

Developed by M&I Materials in the 1970s, MIDEL 7131 is the superior alternative to mineral oil. Its effectiveness is demonstrated up to 433kV and is widely used in 70% of countries worldwide.

Midel 7131 synthetic ester

MIDEL 7131 synthetic ester

premium performance since the 1970s

  • MIDEL 7131 is a biodegradable synthetic ester dielectric liquid designed to provide an alternative to mineral oil, silicone liquid and dry-type transformers.
  • MIDEL 7131 has a high fire point (316˚C), significantly increasing the fire safety of your transformers and reducing the need for fire protection equipment.
  • MIDEL 7131 is readily biodegradable, avoiding environmental damage should leakage occur and enabling reductions in containment measures.
  • MIDEL 7131 has an extremely low pour point of -56˚C, making it a highly effective solution in colder climates.
  • MIDEL 7131 has exceptionally high moisture tolerance. This characteristic enables the extension of cellulose insulation life.
  • is currently used in a wide range of transformer applications and is proven up to 433kV. Perfectly suited for non free-breathing and free-breathing transformers (due to its excellent oxidation stability) located indoors or outside.
  • offers the ability to safely increase transformer loading or reduce transformer size.

Transformer fires are frequent in global power networks. These fires spread quickly, causing extensive damage and sometimes resulting in loss of life. MIDEL 7131 effectively mitigates the risk of fire. It is widely specified and used worldwide, with a flawless fire safety record since its introduction in the 1970s.

MIDEL’s engineers and chemists have developed strong partnerships with end users and leading transformer manufacturers. The team actively participates in working groups of IEEE, CIGRÉ, and IEC, and collaborates with industrial associations and academic institutions on extensive projects. This extensive experience enables the MIDEL team to offer unparalleled technical guidance.

MIDEL 7131 – Protecting lives, the environment and property since the 1970s

Developed in the 1970s, MIDEL 7131 is today used in thousands of new transformers to increase safety. Over the same period, MIDEL 7131 has gained an excellent reputation as a cost effective retrofill fluid for the replacement of flammable mineral oil.

•100% fire safety record
•High fire point (>300°C) – K class classification
•K3 classification (IEC 61039)
•Suitable for indoor, outdoor and underground installations

•Readily biodegradable
•Not detrimental to activated sludge in biological treatmentplants

•Very low pour point: -56˚C

•Absorbs large amounts of moisture with no reduction of breakdown voltage (up to 600ppm)•Allows moisture to migrate from cellulose into the fluid, thus extending cellulose life
•Very high saturation limit (2,700 ppm @ 20˚C) making precipitation of free water virtually impossible

•Superior oxygen stability
•Flexible – used in non free-breathing and breathing systems
•Proven up to 433kV
•High performance in cold climates

•Allows for compact transformer design
•Option to run at a higher temperature, for a standard lifetime
•Provides a higher power output, without the need for high temperature insulation

If you are searching for the latest MIDEL 7131 MSDS, Safety Data Sheet, SDS, please click on this link.

Related Downloads

You can download more Case Studies of MIDEL 7131 here