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Specialist Materials for Industry and Science

Moisture Tolerant

Moisture Tolerant

MIDEL 7131 is one of the most moisture tolerant transformer fluids available. It will absorb far more water than mineral oil and even natural ester without compromising its dielectric properties.

Moisture is known to accelerate cellulose degradation which in turn is a significant factor in transformer lifetime reduction. MIDEL 7131 has the potential to keep cellulose drier, thus extending the life of the transformer.

Moisture tolerance is particularly important in areas with high humidity or risk of moisture ingress. Mineral oil can become saturated with small amounts of moisture, reducing its effectiveness as a dielectric fluid but MIDEL 7131 can tolerate substantially larger amounts of moisture in comparison and still work effectively.

If you are concerned about the effect moisture can have on your transformer, MIDEL 7131 fluid can provide the perfect solution.

MIDEL 7131 for Superior Moisture Tolerance

  • Absorbs large amounts of moisture with no reduction of breakdown voltage (up to 600ppm)
  • Allows moisture to migrate from cellulose into the fluid
  • Potentially keeps the cellulose drier and slows the rate of ageing
  • Very high saturation limit making precipitation of free water virtually impossible
  • Reduces risk of bubble formation
  • Retrofilling*

*Field trials conducted by M&I Materials show that MIDEL 7131 can be used to bring transformers with very wet cellulose back into operation by a simple retrofilling procedure. One particular mineral oil filled distribution transformer was going to be de-commissioned due to high moisture levels; a retrofill with MIDEL 7131 brought it back to a state of safe operation. More than 5 years later, the unit is still in perfect working order and has not required any further maintenance.

For further information please visit our Documents or Contact Us.



  • Apiezon
  • Metrosil
  • Midel
  • Wolfmet

Products of M&I Materials Ltd.