Natural ester fluids: New tool for transformers

When natural ester fluids first came on the market as a coolant and insulating fluid for transformers in 1998, they were seen primarily as a “green” alternative to mineral oil. Because they are typically more expensive than mineral oil, their usage was limited primarily to installations where environmental or fire safety was at a premium.

A recent trend, has emerged, however, that shows utility companies are increasingly turning to natural ester fluids to help them capture the operating efficiencies they need to remain competitive.

In 2013, CPFL Energia, the largest privately owned energy company in Brazil, announced that it would begin changing all of its transformers to a natural ester fluid coolant and insulator. CPFL’s distribution network serves roughly seven million customers in 569 towns and cities in southern Brazil. Earlier this year, the largest natural-ester-fluid filled power transformer in the world was brought on line when Transnet BW commissioned a 420 kV substation transformer filled with natural ester fluid at its Burchsal-Kàƒ¤ndelweg substation.

And in June, Tata Power — India’s largest integrated power company — announced that it will use natural ester fluid in its new packaged substation transformers across the Mumbai distribution area. Tata Power serves more than a half a million residential and industrial customers. Like Transnet BW and CPFL Energia, Tata Power selected Cargill’s Envirotemp FR3 fluid (the most widely used natural ester fluid) for its transformers.

These companies are just a few of the many that are finding that natural ester fluids are no longer a niche product, but rather a new tool that can help them capture real value in an ever-changing marketplace. To date, more than 100 U.S. utilities—including a major power company in northern California that maintains roughly a million transformers in its distribution system—have made substantial investments in transformers filled with natural ester fluids. And dozens more are considering following in their footsteps. In part, they’re doing so simply because they now better understand the advantages natural ester fluids offer compared to mineral oil.

Natural Ester Fluids Gain Understanding, Verification

During the past two decades, natural ester fluids have demonstrated — through usage in the marketplace and through public and private research studies  — that their performance more than offsets the added cost relative to mineral oil.

When it comes to the environment, natural ester fluids perform as expected. According to Environmental Protection Agency guidelines, natural ester fluids are deemed to be “ultimately biodegradable” (meaning they will completely biodegrade in 28 days).

They have been classified as non-toxic and non-hazardous in soil and water by the Organization for Economic Cooperation and Development. The carbon footprint for natural ester fluids — which have been determined to be carbon neutral through a BEES 4.0 lifecycle analysis — results in 56 times less carbon emissions than mineral oil.

Additionally, there are now industry standards in place to help utilities adopt and integrate natural ester fluids in the power industry; ASTM, IEEE, and IEC, for example, all have published standards for natural ester fluids.

More importantly, in the eyes of power company business managers, natural ester fluids’ other characteristics are being proven more valuable than once believed. Consider the following natural ester fluid facts:

“-          Their flash point and fire point are more than twice that of mineral oil. They are self-extinguishing — which mitigates the risk of pool fires — and they have been classified as less flammable by Underwriters Laboratory and FM Global. As a result, natural-ester-fluid filled transformers can be placed closer to one another and to buildings, which facilitates easier space-constrained installations. And, they have the potential to eliminate expensive fire walls and deluge systems.

“-          They can absorb roughly 10 times the amount of water that mineral oil can. This protects the cellulose insulation in the transformer from degradation, which makes the system self-drying and can extend the insulation life by five to eight times more than mineral oil—which in turn can extend the life of the transformer.

“-          New transformers filled with natural ester fluid can operate at higher temperatures — 130ºC hot spot versus 110ºC — with the same life expectancy as mineral oil transformers. This means power companies could specify their ratings and design parameters and opt either to keep the same size transformer and re-rate it to a higher power capability — or design a smaller transformer with the same power capability.

These capabilities give power companies a lot more flexibility and create new options for capturing value and operating efficiencies. What’s more, new regulations and new market demands are offering even more options for modern day power companies.

Market Changes Tip the Scales

In some geographic areas, new regulations have been established or are being considered. The Bureau of Land Reclamation now requires the use of a transformer coolant and insulator at several hydroelectric dams that will cause no significant environmental damage.

The aging infrastructure of the power industry also may be creating incentive for power companies to consider using natural ester fluids. Currently, the average age of power transformers in the U.S. is about 50 years old. The ability of natural ester fluids to potentially extend the life of transformers helps offset the added up-front expense of a retrofill. What’s more, the Federal Energy Regulatory Commission recently ruled that — because natural ester fluids have been determined to extend asset life — all costs associated with the conversion to them (fluid, labor, and equipment) may be capitalized.

The Department of Energy is also in the process of developing more stringent efficiency requirements for transformers — a change that could force manufacturers to use different core steel, potentially increasing their weight by 30 percent. This could create a number of new challenges — and expenses — for the power industry around the need for sturdier equipment, more demanding installations, and so forth. Because of their higher loading capabilities, natural-ester-fluid-filled transformers could handle these more stringent requirements without increasing the size and weight of transformers.

Finally, consumers around the world are increasingly demanding safer, more reliable, and cleaner energy — and the renewable chemistries and capabilities associated with natural-ester-fluid transformers may be a good option to meet that demand. And this, too, helps companies capture real marketplace value. After CPFL Ernergia in Brazil made the switch to natural ester fluids, Caius Vinicius Sampaio Malagoli, CPFL manager of maintenance and standards reported the changes his company experienced.

“The switch to natural ester fluids has produced immeasurable value to our brand, peer acknowledgment, and interest in our company,” he said.

Author: David S. Roesser has over 20 years of experience in R&D, new business and product development, marketing, sales and business management. He is currently Global General Manager Dielectric Fluids for Cargill’s Industrial Specialties business unit. In this capacity he is primarily responsible for the P&L, growth, management and development of Cargill’s Global Dielectric Fluids Business.

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The Clarion Energy Content Team is made up of editors from various publications, including POWERGRID International, Power Engineering, Renewable Energy World, Hydro Review, Smart Energy International, and Power Engineering International. Contact the content lead for this publication at

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