The Benefits of FR3 Fluid vs. Mineral Oil for Distribution Transformers

By Chris Davis, Senior Market Specialist – Electric Utility

FR3 fluid has been around since the early 1990s and is the primary alternate dielectric fluid to mineral oil in the United States.

While FR3 fluid does have a higher first cost than mineral oil, the benefits far outweigh the initial cost difference.

Benefits of FR3 fluid over mineral oil

1. Higher flash point and fire point

FR3 fluid has a flash point of 330° C and a fire point of 360° C, while mineral oil has a flash point of 155° C and fire point of 165° C. These higher numbers mean that a transformer has a lower risk of catching fire with FR3 fluid.

FR3 fluid is also classified as non-propagating. This means it is self-extinguishing and won’t continuously burn if ignited.

2. Extended insulation paper life

FR3 fluid can extend the life of insulation paper in the transformer. Accelerated life tests show FR3 fluid can extend paper life up to eight times longer than mineral oil under standard loading conditions. This greatly reduces the total life cycle cost of a transformer.

3. Increased overload capability

FR3 fluid increases the overload capabilities of the transformer and allow transformers to be overloaded by 14% with no loss of life. The overload capability of FR3 fluid allows transformers to be smaller and utilize a more optimized design.

4. More environmentally friendly

Finally, FR3 fluid is 100% biodegradable and has over 99% biodegradation within 28 days. FR3 fluid is a natural dielectric fluid derived from vegetable oil and is reclaimable and recyclable. It doesn’t contain any petroleum, halogens, silicones or sulfurs.

FR3 fluid is nonhazardous and nontoxic in soil and water. Since FR3 fluid is much more environmentally friendly, you can save a lot of money in remediation costs if there is ever a spill.

Disadvantage: Pour point

The one drawback of FR3 fluid is it has a higher pour point than mineral oil. Where the pour point of mineral oil is below -40° F, the pour point of FR3 fluid is -6° F.

However, this doesn’t mean FR3 fluid can’t be used in areas that reach temperatures below -6° F, as the heat generated from the transformer is generally enough to keep fluid temperatures above the pour point.

Once FR3 fluid goes below its pour point, it will start to gel. The higher viscosity of the fluid can potentially restrict the operation of moving components.

But even if FR3 fluid starts to gel, it is still able to flow below its pour point. FR3 fluid retains its dielectric strength to at least a temperature of -58° F.

We’ve had a couple customers in cold, high elevation regions experience issues with FR3 fluid. However, those instances involved transformers in remote areas with very little load, and they occurred when the temperature remained significantly below FR3’s pour point for several days.

At the same time, we have customers who see temperatures below -30° F that haven’t had issues with FR3 fluid.

Want longer transformer life? Choose FR3

Choosing FR3 fluid can extend the life of your transformer and increase safety. The higher cost of FR3 fluid compared to mineral oil is offset by these benefits.

To learn more about FR3 fluid options for your service area, reach out to an account manager at your local Border States branch.

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