A new lease of transformer life: five reasons to retrofill


Catastrophic transformer fires and downtime could be avoided if critical sites move to the use of ester fluids. Midel’s Barry Menzies presents the case for making a change.

Factories, hospitals, universities and airports are all very different facilities with very different energy demands, but they have at least one thing in common: for each of them there will be someone lying awake at night worried about transformer failure.

The recent Midel Transformer Risk Report (TRR) indicated that more than 80% of professionals working with transformers worry about a failure, with half predicting a significant effect on operations in the event of one.

With safety and business continuity in the balance, it is vital for asset managers to ensure their transformers remain fit for purpose as they age, and as the demands placed on them (and the built environment around them) increase. However, replacing a transformer can be an expensive and disruptive process. If only there was a way to upgrade or prolong the life of a transformer in situ…

Enter retrofilling

Retrofilling is the process of draining and replacing the transformer’s insulating liquid. Typically, the liquid being replaced is mineral oil – the go-to transformer fluid for much of the market due to its low price and adequate performance in most business-as-usual scenarios. The replacement is usually an ester fluid, which offers a number of advantages. Generally, any distribution networklevel transformer previously filled with mineral oil can be straightforwardly retrofilled with an ester fluid (some technical considerations apply). But what are the reasons to do so?

Reason one: safety, safety, safety
Mineral oil has a relatively low fire point at 170°C, at which point it can potentially ignite and cause dangerous pool fires if the transformer ruptures, as evidenced by the host of transformer fire videos on YouTube or Google. Ester fluids, by contrast, are K-class fire-rated, meaning their fire points are at least 300°C, drastically reducing fire risk.

Even in the event of a failure, ester-filled transformers will not cause pool fires. As such, retrofilling with esters can provide a major safety upgrade – the number one concern of any asset manager. This is especially important for transformers in sensitive locations, such as within hospitals, in the proximity of flammable materials, or near the general public.

You might wonder why mineral oil would have been used in these locations in the first place (we have even seen a mineral oil transformer in the basement below a maternity ward – it has since been retrofilled with ester fluid). It is a matter of awareness and education; the fact is, in past decades there were few well- known alternatives to mineral oil, making it the only option by default. However, attitudes to risk change and esters are now well known and widely available.

Retrofilling, where technically possible, is a cost-effective way to improve safety compared with replacing the transformer. When it comes to safety, the bottom line is that ester fluids are an accepted technology, so the decision to use mineral oilin a transformer is a decision to accept a higher degree of risk.

Reason two: asset life extension
Another major concern of any asset manager is to prolong
the life of their assets and thereby extract maximum value from them. Transformers are expensive and having to replace one before it is absolutely necessary is a difficult proposition to make to the finance director.

Retrofilling with esters can help by prolonging the transformer’s lifespan (and in some cases enabling the transformer to operate under increased load). One of the key factors that drives ageing in transformers is water, which can ingress from the atmosphere, or be produced during paper ageing processes. This water then accelerates the degradation of the solid insulation material. Esters, however, have a far higher moisture saturation point than mineral oil, meaning they can absorb more water.

This effectively keeps the solid insulation drier, which reduces its rate of degradation, thereby slowing down the paper ageing process and prolonging transformer life. In theory, esters can give a 5-7 times increase in insulation longevity in this way. It is realistic to expect insulation life extension of between 25 and 50% (if not more) – music to a finance director’s ears.

Reason three: A powerful financial case

There are other financial benefits to retrofilling beyond asset life extension, too. One is concerned with insurance. Certain insurers such as FM Global have studied the risks related to transformer fluids and now specify what they call “less flammable fluids” in certain circumstances, rather than mineral oil. As such, retrofilling with esters may be the difference between a policy renewal being approved or rejected, or open up more choice between insurers on the market. In some instances, it may even lower premiums.

Retrofilling can also be useful from an accounting point of view. Along with finance directors, asset managers must always play a juggling act between capital and operational expenditure (capex and opex). If upgrades are required to the transformer fleet but there is insufficient capex budget to replace all transformers, others can potentially be retrofilled from the opex budget, thus delivering the benefits of ester fluids immediately, without capital outlay. Both benefits should be attractive to any finance director. 

Reason four: Better for the environment

Another drawback of mineral oil is that it is both toxic and non-biodegradable. In the event of a leak it can damage the local environment. For transformers placed near fragile ecosystems or water sources, such damage can potentially be significant.

As with health and safety, our society-wide attitudes to risk have evolved in the decades since many of these transformers were first installed. While these risks may once have been deemed acceptable, they are less likely to be now. For any transformer-operating firm with a robust CSR programme or other commitment to the environment, retrofilling with non-toxic, biodegradable esters is an appealing option. For example, in the 1990s European utility Vattenfall embarked on a transformer retrofilling initiative in Berlin. The city presents very specific challenges for transformer installations since much of the city is zoned as water protection areas, requiring safeguards regarding spillages of hazardous materials, including mineral oil. To date more than 1,200 distribution transformers in the city have been retrofilled with ester fluid.

Reason five: Bolstering reputation

Improving health and safety and environmental performance with ester fluids are worthy goals in themselves. However, there is extra value to be had in the reputational boost these efforts offer. A proactive communications campaign built around a retrofilling programme can help a company boost its reputation to its customers and other stakeholders.

Conversely, there is a significant reputational risk that comes with a major safety or environmental incident. It may seem ‘softer’ than the hard numbers of the financial argument, but a responsible board will be mindful of such events damaging the company – not to mention any negative impact it may have on its business performance 

 Ready to retrofill

It’s true that all transformers will eventually need replacement whether they are retrofilled or not, and a company may have its own reasons for investing in new assets rather than extending the life of the existing fleet. However, since retrofilling brings so many benefits, why not extend asset life with ester fluids, especially when doing so is likely to more than offset the investment?

The actual retrofilling process is minimally disruptive, and can often be completed within eight to 12 hours – easily within the timeframe of most planned maintenance schedules. Normal production or operations are usually hardly affected. It is a simple, proven process with minimal risk involved, if all safety procedures are observed, and is usually performed by oil service contractors. For almost any company operating one or more distribution network transformers filled with mineral oil, the case for retrofilling with ester fluids is compelling. For a relatively low investment per transformer, the company can bolster its business continuity strategy and enjoy major safety, environmental and financial benefits by giving their transformers a new lease of life.


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