Dielectric Technology in Transformer

Utilities and transformer manufacturers focus on the design and manufacture of environmentally-friendly transformers that are nonhazardous while offering improved life cycle costs with minimal maintenance. These transformers offer reduced carbon footprint, reduced levels of pollution (water, soil, noise), enhanced lifecycle costs, enhanced product lifetime, and enhanced fire safety…

In all power distribution networks, transformer is an important part of system. Utilities and transformer manufacturers focus on the design and manufacturing of environment-friendly transformers that are nonhazardous while offering improved lifecycle costs with minimal maintenance. These transformers offer reduced carbon footprint, reduced levels of pollution (water, soil, noise), enhanced lifecycle costs, enhanced product lifetime, and enhanced fire safety.

As according to research analysts, the top three emerging trends driving the global liquidimmersed power transformers market are:

• Evolution of eco-efficient transformers
• Environmentally friendly and fire-resistant insulating liquids
• Transformer going intelligent.

The various transformer manufacturers focus on their R&D for the development of transformers that operate insulating liquids which are different from crude base. The research for alternatives fluid led to interesting classes of insulation fluids such as, silicone liquid, synthetic ester and Natural Ester fluids.

As mineral oil is the most commonly used type of transformer insulating medium for more than a century, it facilitates good dielectric transfer property. However, there are some concerns related to the use of mineral oil in transformers. It has a very high carbon footprint and a very low fire point, lying in the range of 150°C to 160 °C which makes it more fire prone. We have enough examples of transformer fire accelerated due to mineral oil globally.

Now-a-days, Natural Ester fluid technology getting popular due to its inherent advantages like its higher thermal capability improves capability of insulation paper & life of transformer. These are in conformity with standards like, IEC 60056, IEEE C57, IEEE 637, ASTM D6781 and IEC 60296.

Natural Ester Fluids: In the early 1990s, natural ester made an appearance. It is made of plant seed oils (e.g. soybean). These can be broken down into saturated, single, double and triple unsaturated fatty acids. The main advantages are significantly higher fire points (360°C) and the best biodegradability. One of the best examples of Natural Ester is Envirotemp FR3 dielectric fluid.

Utilization of Natural Ester fluid is on the rise owing to the increased safety against fire hazards and eco-efficient solution. Natural Ester fluid is incombustible and it possesses non-toxic attributes, which has boosted its increasing popularity and use in transformers. The advantages offered by Natural Ester over mineral oil are as follows:

• Offer higher flash/fire points
• Biodegradation of Esters is much better as compared to mineral oil or silicone liquid shown in (figure 1).

Figure 1: shows the good biodegradability of ester based insulating fluids (CIGRE SC A2 reports)

Key optimization options for advantage with Natural Esters that leverage the insulation life extension and thermal capabilities of FR3 fluid.

1. Increase load capacity:

A second option is to use the same life but gain more load capacity. This is useful in situations where cannot put in a larger transformer either due to space constraints or cost. You can get more power out of the same asset. Also, this is a great option for retro fills. This does not require any changes to your standard transformers. It can be used the same transformers and know there is approximately up to 20% more load capacity.

2. Life extension:

By protecting the insulation life of the paper, you could then likely extend the life of the asset (depending on the transformer loading profile). This allows to use the same kVA, but can get more useful life out of the existing asset. Thus, it helps in lowering your total cost of ownership. This does not require any design changes to your existing specifications.

3. Smaller Transformer

This third option enables a transformer to be built with a smaller footprint, yet have to maintain the original capacity needed. Often times, this allows an initial cost savings as well given you likely will use less raw materials (copper, paper, steel, fluid, etc.). This would require design changes.

Figure 2: High temperature curve based on Thermally Upgraded Kraft (TUK) paper.

The earliest Natural Ester fluid-filled transformers were new designs built and installed in early 1990 followed by Retro-filling. These early units led the way for many new and retro-filled transformers that presently number over million. The Natural Ester-filled power transformers include power substation units in the range of 6 kV to 420 kV. Few Examples:

Transnet BW: A transmission network operator in the German state of BadenWürttemberg – commissioned a 420kV power transformer in one of its substations in southwest Germany that is cooled and insulated with Natural Ester FR3. The substation, which has a power rating of 400 MVA is the first in this highvoltage category has been working satisfactory since 2013 (OEM Siemens).

1. Electronorte Brazil: 22.14 MVA, 242KV, 3ph. reactor KNAN cooling class, new transformers manufactured in June 2007 by Areva Brazil and commissioned in March 2009.

2. Petrobras refinery chooses FR3 fluid for improved fire safety: Petrobras Northeast Refinery Project “Abreu e Lima”.14 Transformers using Envirotemp FR3 dielectric fluild. A.75/100MVA, 242/72.5 KV -2 transformers.

B.70MVA, 72.5/15/15 KV – 4 transformers
C.45/60MVA, 72.5/15KV 8 transformers.

3. Tata Power: One of the green milestones in the company’s centenary year celebrations, two of India’s first 25 MVA natural ester filled transformers were installed in Mumbai. With this initiative, Tata Power has once again showcased its priority in driving sustainability by implementing path breaking green technology. Sustainability remains a core business philosophy of Tata Power, and green transformer is one of the company’s many green initiatives under its ‘Be Green’ campaign. Tata Power’s 25 MVA transformer filled with Natural Ester Enivrotemp FR3 Dielectric fluid. (OEM Schneider India)

4. GETCO (Gujarat Electric Transmission Company): Installed transformers with natural ester fluid FR3 & after satisfactory on site performance has decided to go in big way with almost 200 plus 66KV, 20MVA units (OEM T&R and Atlanta). Transformers will be tested for its higher thermal class as per IEC 60076 part 14, Table C.2.

5. Torrent Power: Two numbers of 20 MVA, 33/11 KV having KNAN/KNAF cooling class Manufactured by T&R India in December 2016.


Transformer manufacturers are designing Natural Ester fluid-filled transformers that operate within the temperature limitations outlined in IEEE/IEC and other international standards while providing access to the thermal capabilities. Utilities are improving performance by adopting Natural Ester fluid and changing their usage profiles.

Now that the Indian Standard IS-16659 On Unused Natural Esters is published, the progression of the use of natural ester insulating liquids is now starting the “acceleration”. After providing excellent performance in power transformers (up to 440kV) for many years, currently, there are a number of 550 kV projects and higher under study. The transformer made by Siemens Germany for Transnet BW with Envirotemp FR3 Natural Ester has opened further market & voltage class.

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