ANSWER:

There are a range of MIDEL fluids to suit all types of transformer preservation systems.

For breathing transformers, we recommend the use of MIDEL 7131 which is oxygen stable and suitable for continuous contact with air. For non-breathing transformers either MIDEL 7131 or MIDEL eN 1204 can be used. Typical transformer designs meeting the “non-breathing” classification include:

• hermetically sealed design with expandable radiators/corrugated tanks

• oil conservator design or retrofitted with a bladder/diaphragm/air seal, and

• designs with nitrogen or air head spaces incorporating pressure relief devices

When is oxidation a concern?

Natural esters have a much lower level of oxidation stability than other liquids and if exposed to oxygen they can increase in viscosity over an extended time. This can reduce the cooling efficiency of the transformer, leading to an increase in operating temperature. For this reason, natural ester-based products are not recommended for breathing type transformers, where the liquid is continuously in contact with air.

For free breathing transformer applications, we recommend MIDEL 7131.

MORE READING:

Read more on oxidation and ageing of insulation:

More questions on ester fluids?

This post is one of the 15 top questions we get asked on retrofilling transformers with ester fluids. Here is the full list of the frequently asked questions on ester fluid retrofilling:

1. Miscibility: Which transformer oils are compatible with Midel ester fluids for retrofilling?

2. Free-breathing: Can I use Midel fluids in breathing transformers?

3. Insulation Regeneration: Will Midel fluids heal existing problems in a transformer?

4. Fire Safety: Which dielectric fluids classifications are important to understanding fire safety?

5. Cold Weather: How do Midel fluids perform in the cold?

6. Moisture: What happens to the performance of Midel fluids when they absorb moisture?

7. Acid Levels: If Midel fluids have high acid levels, how do I recondition my fluid?

8. DGA: How can I use dissolved gas analysis on Midel fluids?

9. Power Factor: What is the Power Factor of Midel fluids?

10. Materials Compatibility: Are Midel fluids compatible with all transformer materials?

11. HV Applications: Can I use Midel fluids to retrofill transformers at high voltages?

12. Interfacial Tension: Is interfacial tension a meaningful property for Midel fluids?

13. Reusability: How are used Midel ester fluids processed and handled?

14. De-rating: Will there will be any derating of a transformer by changing it from mineral oil to a Midel ester fluid?

15. Retrofill Process: Are there extra requirements or steps when retrofilling transformers with Midel fluids?