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TOP 15 QUESTIONS

Retrofilling transformers with FR3 Fluid

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Why retrofill a transformer? The motivations for power and distribution transformer retrofilling are numerous. They range from addressing an urgent need on a single asset, to rolling out a network-wide program with clear financial returns.

Each transformer has unique operational factors that influence the situation such as load, asset design, age, location, and environment.

Transformer insulation: the weakest link In many cases, the reasons relate to the cellulose insulation, since this is the weakest link in a transformer. Cellulose insulation failure is one of the top three reasons for a transformer failing and degradation of the insulation (ageing) is irreversible.

Some of the most common reasons for transformer retrofilling include:

OIL QUALITY decrease the levels of undesired

contaminants and dissolved gases

DRY OUT reduce moisture levels in the oil

PCB CONCENTRATION remove contaminated oil

EXTEND USEFUL LIFE and delay replacement

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When retrofilling mineral oil filled transformers with Envirotemp FR3 natural ester fluid, there are additional financial incentives that support positive return on investment. This is due to the unique capabilities of FR3 fluid and its performance in transformers, resulting in cost savings without sacrificing reliability.

LIFE EXTENSION significantly beyond what is

possible with mineral oil

SLOW THE AGEING RATE and delay capital investment for

transformer replacement

INCREASE LOAD additional load capacity within the

existing transformer footprint

OVERLOAD CAPACITY gain increased safe overload

FIRE SAFETY reduced risk through much higher

fire point and flash point

SAFETY COMPLIANCE meet fire codes, insurance audits;

clearances, fire wall, deluge system

+

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ENVIRONMENTAL IMPACT minimise environmental impact and facilitate policy compliance

SPILL REMEDIATION simplified and less costly bio

remediation and containment Many of our customers have financially justified FR3 natural ester fluid retrofills based on just one of these factors. When multiple factors are evaluated together, they can create very compelling business cases for retrofilling with FR3.

Positive return on investment Retrofilling mineral oil filled transformers with FR3 fluid can deliver a positive return on investment. Some of the contributing factors include:

• Additional 20°C tolerance provided without accelerating normal insulation system aging rate (achieved through additional loading)

• Fire mitigation equipment can be removed from service, eliminating some maintenance expenses

• Costs incurred to remediate future spills may be reduced • Reduced risk of dielectric failure caused by bubble formation

during overload • Reduced risk of collateral damage to other equipment by not

incurring dielectric pool fire • Avoid capital expenditure on costly site works, such as fire walls

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Many mineral oil filled transformers are being pushed to carry load beyond nameplate rating even though the exact condition of their cellulose insulation is unknown. Such practices accelerate the aging of the paper insulation, potentially reaching end of life.

Fortunately, replacing the old mineral oil (retrofilling) with natural ester fluid is a cost-effective way to slow the thermal aging rate of insulation, enabling increasing load-ability of transformers.

A better understanding of FR3 for retrofill We get a lot of questions on FR3 and natural ester fluid – especially when it comes to retrofilling transformers. That’s why we’ve put this guide together on the top 15 questions (and answers) – to help organisations better understand the challenges and possibilities of retrofilling with FR3, and assist them to make investment decisions with greater certainty.

Turn the page to see the top 15 questions on retrofilling transformers with FR3 natural ester fluid.

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#1 Fluid miscibility Which transformer oils are compatible with FR3 fluid for retrofilling? Compatible: Mineral oil, R-Temp, synthetic ester

Not-compatible: Silicone

Extensive laboratory testing and field experience has confirmed excellent miscibility and overall retrofill compatibility for FR3 natural ester fluid with conventional mineral oil and high temperature hydrocarbon fluids (i.e. R-Temp fluid). FR3 fluid is not miscible with silicone and should not be applied in transformers previously containing silicone.

While FR3 fluid is miscible and compatible with conventional transformer mineral oil, it is important that the fluid be maintained in as pure a state as when new, to avoid decreasing the performance and environmental benefits.

Unlike most other fluid types, the residual transformer oil in a properly retrofilled transformer should not reduce the fire point of Envirotemp FR3 fluid below the NEC minimum of 300°C. Thus, mineral oil content of up to 7% does not impact fire point (keeps fire point above 300°C).

Read more on miscibility and transformer oil compatibility in the Envirotemp FR3 fluid datasheet

Get more detailed retrofilling guidelines for power and distribution transformers

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#2 Free breathing Can I only use FR3 fluid in hermetically sealed transformers? FR3 fluid is recommended for use in ‘non free breathing’ transformers. Restated, FR3 fluid is not recommended when the fluid stays in continuous contact with ambient air (for example, in transformer designs with oil conservators without a bag). If the exposure is not continuous, but eventual or rarely, or if the oxygen availability is limited (confined air), the solution is acceptable. Typical transformer designs meeting the ‘non free breathing’ classification includes:

• hermetically sealed designs with expandable radiators/corrugated tanks

• oil conservator designed or retrofitted with a bladder/diaphragm/air seal, and

• designs with nitrogen or air head spaces incorporating pressure relief devices

Even in a true free breathing design, the oxidation of FR3 fluid will occur over a long term, measured in years. The real result of extreme FR3 fluid oxidation is an increase in viscosity. Over time, there is potential that the viscosity of FR3 fluid will increase to an unacceptable level, impacting heat transfer capabilities, before the anticipated life of the transformer; hence, FR3 fluid is not recommended in true free breathing transformer.

See this article on Oxidation of transformer oils and how FR3 natural ester compares in the laboratory and in field

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#3 Insulation regeneration Will FR3 fluid heal existing problems in a transformer? No. FR3 fluid cannot “regenerate” insulation materials Degradation (or ageing) of the solid cellulose insulation is irreversible. Thermal ageing of the paper cannot be avoided – however it can be slowed. By retrofilling with FR3 fluid, the “remaining life” of the transformer will be extended by a reduction of ageing velocity at the same operation temperature.

As the above image shows, FR3 fluid is proven to protect the insulation paper 5-8 times longer than mineral oil. That extends asset life, reduces total cost of ownership and improves grid reliability.

So how exactly can the ageing process be slowed with FR3 fluid? Find out here.

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#4 Fire safety classifications All materials burn, so which fire safety tests are important? The classification of insulating liquids pertaining to fire safety and designation “less flammable liquids” is dependent upon fire point alone.

A “K-Class” fluid possesses a fire point greater than 300°C. For transformers, international standards and fluid designations by fire laboratories and insurance companies declare “approved transformer fluids are those that have a fire point greater than 300°C” (i.e. K-class fluids). Fire point is the determining fluid characteristic to eliminate the potential for a transformer (pool) fire.

What does this mean for FR3? There has never been an oil fire reported in over 1 million installations over the past 20 years.

Want more information on how you can improve your fire safety? Here’s why you should retrofill with FR3.

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#5 Cold weather How does FR3 fluid perform in application at cold temperatures? FR3 fluid is recommended for all transformers, regardless of ambient temperature, where the oil is not in direct contact with outside air. FR3 fluid maintains breakdown voltage equivalent to mineral oil, down to -50°C, as shown in the graph below.

Cargill recommend using start-up procedures similar to those recommended for mineral oil filled transformers (refer IEEE C57.93 or IEEE C57.106; there is no known equivalent in IEC – a CIGRE Workgroup is being formed in 2017).

For applications where devices require mechanical movement to complete their function (i.e. switches and circuit breakers), the transformer should be warmed to at least -10 °C, as FR3 fluid can inhibit physical movement of the device at very high viscosities.

The behaviour and dielectric performance of FR3 in cold temperature environments in addressed in full in this article.

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#6 Moisture Since FR3 fluid attracts moisture, how does that impact performance? FR3 fluid doesn’t “attract” water (moisture). It has a higher saturation point than mineral oil, and it is more tolerant of water than mineral oil. At room temperature, FR3 fluid can dissolve about 1000 mg/kg of water to become saturated compared to 60 mg/kg for mineral oil.

So, what happens inside the transformer? Water moves between the solid insulation and oil trying reach equilibrium (relative saturation). Paper produces water as a by-product of thermal aging, which acts as a catalyst for continued degradation.

Because mineral oil is hydrophobic, the water stays in the paper.

Since Envirotemp FR3 fluid is comparatively hydrophilic, water is absorbed by the fluid or wicked away from the insulation paper.

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Hydrolysis of natural ester “consumes” the water and produces fatty acids. This process removes dissolved water.

FR3 fluid is in essence “self-drying”. Water concentrations in the fluid will be reduced to hydrolysis over time. More here.

What does this mean for transformer life?

So, in general, an insulation system will be dryer (lower % saturation) with natural esters. Subsequently, the solid insulation system will age more slowly when it is dryer. Natural esters, in effect, dry out the transformer.

As a result, IEEE C57.154 and IEC 60076-14 (high temperature insulation systems) validates the enhanced aging capabilities of FR3 fluid, declaring an FR3 fluid filled transformer can run 20°C warmer than mineral oil while not accelerating aging.

By comparison, a wet mineral oil filled transformer loses its dielectric strength very quickly.

Read up on FR3 fluid's high temperature capability enabling smaller, more effective transformers with increased loading.

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#7 Acid levels If FR3 fluid has high acid levels, how do I process my fluid? Mineral oil: reactive, short chain acids; can be corrosive

FR3 fluid: non-harmful, long chain acids; transesterification

Because of hydrolysis (the consumption of H20 and production of non-reactive, long chain fatty acids) during the aging process, FR3 fluid will possess higher acid levels than mineral oil.

However, mineral oil produces reactive, short chain acids, which can be corrosive to the transformer interior. FR3 fluid produces non-harmful, long-chain acids. So, “high acid levels” in FR3 fluid isn’t a concern; it proves that the solid insulation system is aging more slowly.

Common transformer oil processing techniques

FR3 fluid can be processed using common (to mineral oil) equipment, materials, and processes, including “reconditioning” (via degassing equipment) and “reclaiming” (using Fuller’s Earth or Bauxite).

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FR3 can strengthen the insulation paper

Furthermore, high acid levels in FR3 fluid from hydrolysis combined with high operating temperature of a transformer has proved to be beneficial to the solid insulation system (cellulose) through a reaction called transesterification. While secondary to hydrolysis, it has a stabilizing effect on insulation aging.

Combination ester attaches to weak points of the cellulose. Molecules formed by hydrolysis attach to the cellulose, strengthening the paper.

More information on paper life, transesterification, and grid reliability.

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#8 Dissolved Gas Analysis Can I perform DGA on FR3 fluid? Yes. In general, the same sampling and analysis procedures can be used with FR3 fluid as with mineral oil. Common DGA ratios can be used as well as a FR3 fluid-specific Duval triangle.

IEEE C57.155 (published in December, 2014) is the ester dielectric fluid dissolved gas analysis standard. There is currently no IEC equivalent standard.

Cargill also has its own FR3 fluid DGA guide, which is based upon thousands of FR3 fluid filled transformer samples. It addresses questions such as:

• What should I expect when I see an FR3 fluid DGA report? • What methods are used to interpret FR3 fluid DGA reports? • What should I remember about DGA?

All transformer produce stray gases (gases produced during normal operation). FR3 fluid produces different stray gases (primarily ethane) compared to mineral oil. Stray gases produced by FR3 fluid have been shown to be predictable and of no concern.

For more on this dissolved gas analysis with natural ester fluids and FR3, see our dedicated FR3 DGA hub.

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#9 Power Factor What is the Power Factor of FR3 fluid? Power factor is the ratio of resistance current to capacitance current in an insulation system. The power factor value depends on, among other things, the level of insulation dryness in new transformers. For operating transformers, changes in power factor can indicate increased levels of moisture or other contaminates in the insulation system. There are several variables that impact power factor measurements, even for new, essentially dry uncontaminated units, including:

• the ratio of solid to liquid insulation • the type of dielectric fluid • coil design • and temperature

Understanding FR3 Power Factor

The dielectric loss characteristics of Envirotemp FR3 fluid, a natural ester fluid, differ from those of mineral oil. The chemical makeup of natural esters has a slightly more polar character compared to mineral oil. This translates into a higher dissipation factor, all other variables equal.

Distribution transformers

The power factor measurements of the distribution system models using FR3 in conjunction with distribution production data indicate that a typical new distribution transformer impregnated with FR3 fluid would have a power factor measurement about 50% higher (0.75% vs. an identical unit impregnated with mineral oil of approximately 0.50%, for example).

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Power transformers

The power factor measurements of the power transformer system models using FR3 fluid were approximately 100% higher than the same models using mineral oil. This higher relative value for the power transformer models is due to the higher ratio of oil to paper in the insulation system being measured.

Power factor increase over mineral oil of various winding-winding insulation models using Envirotemp FR3 fluid.

These measurements, in conjunction with power OEM production data, indicate that a typical new power transformer impregnated with FR3 fluid would have, for example, a power factor measurement around 0.40% vs. an identical unit impregnated with mineral oil of approximately 0.20%.

For more on transformer power factor and FR3, see the FR3 resources page.

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#10 Materials compatibility Is FR3 fluid compatible with all transformer materials? In general, if a transformer component or material is compatible with mineral oil, it is also compatible with FR3 fluid.

A thorough (but not comprehensive) compatibility study has been performed with FR3 fluid and an array of materials/components commonly used in transformers.

When investigating the compatibility of a new material or product, ask the vendor if they have run compatibility tests with vegetable oil. Their response will yield the FR3 fluid response. Transformer manufacturers have the responsibility of verifying the compatibility of their specific materials of construction.

Read the technical report on material compatibility in FR3

Regarding gaskets, Cargill recommend ‘good housekeeping practices’.

Specifically, by the time a transformer is identified as a retrofill candidate, it has probably operated for several years. The condition of the gaskets likely includes wear & tear (swelling from contact with oil), mechanically set (it has taken a ‘set shape’, dried out, cracked, etc). If “not touched”, the gaskets may survive without incident. However, when you retrofill, it is likely the gaskets will be “touched”, either physically or indirectly.

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If the tank and/or the gasket itself (in an aged, set, potentially cracked condition) is moved, the outcome is likely to be less than desirable. This has nothing to do with any interaction with FR3 fluid, but rather the mechanical integrity of the gasket. The same recommendations would apply to a service company flushing/reprocessing/refilling with mineral oil. The outcome is not provoked by the new mineral oil; rather, it is because the aged gasket was directly or indirectly moved.

Tap Changers and FR3 fluid

CTR Manufacturing have developed FR3 fluid-filled tap changers with enhanced performance, based on the oil quenching technology which is 100 years old, and proven. Developing their new FR3 fluid-filled tap-changers, CTR took care that they have a solution that is based on advanced technology but is economical at the same time, which is what their end customers require.

At the same time, they have addressed the issue of today’s great concern about the environment and its protection, meeting the worldwide requirement for the use of biodegradable fluids such as FR3.

Read the Case Study on CTR developing FR3 filled tap changer.

Get the technical report on material compatibility in FR3

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#11 HV applications Can I use FR3 fluid at high voltages? Yes, FR3 fluid can be used at voltages as high as 1800kV Test results, reaching voltages as high as 1800kV on non-homogeneous field distribution, yield the conclusion that FR3 fluid’s BDV and dielectric strength is equivalent to mineral oil in all cases except for extremely divergent geometries (needle to plane), where FR3 yields reduced BDV. This requires further investigation, justifying the current use of safety margins.

The permittivity (dielectric constant) of FR3 fluid (3.2) differs from mineral oil (2.2), affecting dielectric stress distribution. This value must be understood and integrated into the dielectric design of a transformer.

Field experience with the world’s largest FR3 transformer The world’s largest power transformer filled with natural ester FR3 fluid has been operating at the highest voltage level in Germany’s grid for almost three years. Read about it in this Transformer Magazine article.

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#12 Interfacial tension Is interfacial tension a meaningful property for FR3 fluid? Interfacial Tension (IFT) is an effective and sensitive indicator of polar oil contaminants in mineral oil dielectric coolant, but is not regarded to the same degree when assessing the quality of natural esters like Envirotemp FR3 fluid.

The reason is that natural ester fluid is slightly polar on its own and is less affected by small levels of polar contaminants.

None of the natural ester fluid standard specifications in ASTM, IEEE nor IEC use the interfacial tension test method to place IFT limits on natural ester fluids. The D6871 standard states that Interfacial tension performance criteria are being assessed; therefore, requirements have not been established.

Based on the variation inherent in the measurement, the relative polarity of natural ester fluid causing insensitivity to polar contaminants and the lack of appropriate standard specification limit criteria, Cargill does not monitor IFT in its standard testing protocols. Furthermore, Cargill recommends that the emphasis on quality of FR3 fluid should be focused on dissipation factor at 25°C and 90/100°C instead of an inappropriate test method in natural ester fluid standard specs.

For more on the extensive testing regime that FR3 fluid has undergone, download the Test Summary, on our FR3 page.

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#13 Reusability What can I do with my used FR3 fluid? Depending upon the level of degradation, FR3 fluid can be reconditioned and reclaimed, similar to mineral oil. Used FR3 fluid can be recycled (it’s acceptable for use as biofuel feedstock). Used FR3 fluid is of interest to the rendering industry (e.g. companies that pick up used restaurant grease) for recycling into oils, lubricants, and soaps.

Similarly, to the dominant disposal method for used mineral oil, used FR3 fluid can be burned (for heat recovery). If disposing in this manner, we’d recommend, burning a 90% mineral oil / 10% FR3 fluid mix in an industrial boiler.

Because FR3 fluid is biodegradable, if disposed of in landfills, used FR3 fluid will fully biodegrade over time.

Read more on the biodegradability and environmental benefits of FR3 fluid and how it compares to mineral oil.

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#14 Derating Will there will be any derating of the transformer by changing from MO to FR3? No. The rationale for this position would be that due to FR3 fluid’s higher viscosity, in a retrofill, the transformer may run a few degrees warmer than it did with (less viscous) mineral oil.

If (for example) the transformer specification reads ’55 AWR’ and the mineral oil filled unit was factory tested at 54 AWR, it may be the position of the manufacturer that the transformer would exceed the temperature rating. However, this is more than offset by FR3 fluid’s enhanced thermal capabilities (now standardized in IEC 60076-14 and IEEE C57.154, which declare that an FR3 fluid filled transformer can run 15°C (Kraft) to 20°C (TUK) warmer than its MO equivalent and not accelerate aging).

Restated, by amending the transformer specification to include one of the standards noted above, there is no reason to de-rate the transformer.

For more on FR3 fluid thermal capabilities, take a look at the updated brochure for FR3 fluid.

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#15 Retrofill process Are there additional steps when retrofilling transformers with FR3?

Essentially there are four easy steps to follow to retrofill transformers with FR3, as follows:

• Drain the oil • Rinse tank and radiators with FR3 fluid • Drain again and remove dregs / sludge • Fill again using new FR3 fluid

There are two detailed guides from Cargill – for distribution transformers and power transformers, which outline the entire process, including pre-retrofill steps and condition assessment. These documents are further supported by the Storage and Handling guide for appropriate fluid usage.

For more on retrofilling, see the separate guides on: • power transformer retrofill • distribution transformer retrofill and • storage and handling guide

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Still got questions? We hope our Top 15 Questions on Retrofilling with FR3 has been helpful to you. If you’ve got other questions on retrofilling, or FR3 fluid generally, we are more than happy to answer your questions.

Contact us on the details below, visit our website, or browse the FR3 brochure and datasheet, which summarise the key information on FR3.

Contact Insulect Australia, New Zealand, Pacific.

1300 446 565 OR +61 3716 6700

sales@insulect.com

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FR3 Fluid Brochure FR3 Fluid Datasheet