ANSWER:

Using much the same oil sampling and analysis methods you would use for mineral oil. The gasses esters produce during electrical and thermal faults are the same as for mineral oil, but the quantities and relative amounts are slightly different.

DGA with Ester Fluids

A lot of the advice provided for DGA with mineral oil still holds true with esters. It is best to look at trends of results, rather than one off measurements and if possible fleets of transformers should be compared to each other.

IEEE C57.155-2014 is the ester dielectric fluid dissolved gas analysis standard.

MIDEL has a guide to dissolved gas analysis for ester fluids, which addresses questions such as:

• How do mineral oil DGA methods differ to ester fluid methods?

• What should I expect when I see a DGA report for an ester fluid?

• How can I properly analyse DGA results for ester fluids?

What about stray gases?

All transformers produce stray gases during normal operation. Natural ester fluids produce different stray gases, primarily ethane, compared to mineral oil or synthetic ester fluid. These stray gases have been shown to be predictable and of no concern.

MORE READING:

Fluid Maintenance and Dissolved Gas Analysis Guide for Ester-based Transformer Fluids.

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?