A game-changing transformer dielectric fluid

The fluid is nonhazardous, 100% biodegradable, and made from natural esters of edible seeds and soybean oil—and has all of the great characteristics of Askarels, with none of the drawbacks.


In the mid 1990s, Cooper Power Systems developed and perfected a totally new transformer dielectric fluid, patented it, and called it EnviroTemp FR3. The fluid is nonhazardous, 100% biodegradable, and made from natural esters of edible seeds and soybean oil. It has a fire point of 360 C, for NEC “Less-Flammable” classification. It has very high dielectric strength, high thermal conductivity, low coefficient of expansion, and good “lubricity” that helps things like tap changers operate properly.


Image of transformer with UL or FM label certifying suitability for indoor insulation. Courtesy: Joe Guentert

Testing has shown that if there is an accidental spill of the liquid, it will biodegrade 99% within 21 days into water and CO2 (unlike silicone fluid, which will biodegrade 0% in the same span of time). At the end of its useful life in transformer service, the liquid is fully recyclable into products like bio-diesel fuel.


In short, FR3 has all of the great characteristics of Askarels, with none of the drawbacks. Within a few years ABB developed a similar fluid, called Bio-Temp, and other similar liquids from other manufacturers are coming into the market.


NFPA 70: National Electrical Code recognized the new Less-Flammable fluids as appropriate for indoor installations, and NEC Article 450.23 set forth new requirements for the details of the indoor installations.


Transformer manufacturers worked with FM Global and UL to obtain listings of the transformers for indoor installation. NEC 450.23 requirements are simple and straightforward. In order to be installed in a noncombustible building, a less-flammable transformer may be installed where there are no combustible materials stored in the area, and there must be liquid confinement of some sort (which might be nothing more than curbing at the doorways of the rooms). The transformer also must bear either a UL or FM label certifying suitability for indoor installation. More about this great transformer fluid in coming weeks.


In coming weeks, we’ll also discuss how this fluid has made it possible again to safely install liquid-filled transformers inside data centers, and we’ll discuss a new liquid substation transformer that has been specifically designed for data center applications, “hardened” for far greater reliability than any dry-type transformer.

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