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15/03/2018 – News / Transformers / Power Generation / Electricity / Engineering / MIDEL

Playing with fire: The growing threat of the world’s ageing transformer fleets

An underground fire that led to a partial evacuation at Newark Liberty International Airport on 14th January was just one in a series of blazes with a common cause – catastrophic transformer failure. Barry Menzies, Managing Director of MIDEL Dielectric Fluids Global, reports on the growing threat posed the world’s ageing transformer fleet.


With global energy demand on the rise, the world’s transformer fleets – which play a vital role in ensuring electricity flows efficiently – are starting to groan.


The boom years of industrial growth between the 1950s and 1980s brought with them substantial investment in energy infrastructure. But as the global population has continued to grow, the rate of investment in this critical infrastructure has failed to keep pace. 


The average cost of a new transformer has risen by 5.5 per cent annually for around 20 years. This has typically resulted in a 100-per-cent increase in the price of a transformer every 12-15 years. Deterred by this, owners have been postponing capital investments. Rather than upgrading the transformer fleets, they are relying ever more on existing assets to cope with a job that becomes more demanding with each passing year.


Transformer failure – and transformer fires – can occur at any time, but the threat increases as they move through their life-cycle. Under ideal conditions, transformers are expected to operate for 30 to 40 years, while industrial transformers have a life expectancy of 20 to 25 years. As the existing fleets installed during the boom years continue to age, and electricity demand continues to rise, it’s clear that without a change in approach to how these vital assets are maintained, the risk of fire is only going to increase.


A serious blaze


Catastrophic transformer failure can lead to catastrophic fires. At their worst, transformer fires have caused loss of life and significant damage to the environment. 


For as long as there have been transformers, mineral oils have been the go-to dielectric fluid, serving to provide electrical insulation and cooling. Largely, they have been up to the task, boasting excellent dielectric and thermal properties. However, mineral oils have one main drawback: flammability.


When a fire does occur, it can put a transformer out of action, in addition to causing serious damage to the surrounding equipment. This can be particularly devastating in highly-populated areas, where transformers can feed critical assets such as schools or hospitals. Additionally, this could cause a risk to business continuity, potentially causing major disruption and delay to operations. 


Mitigate the risk


While mineral oil still makes up the vast majority of the transformer fluid market share, there is an alternative that minimises the risk of fire. Ester fluids are a fire-safe and biodegradable alternative to mineral oil, and are increasingly being chosen by power utilities and end-users to minimise fire risk.


Compared to mineral oil, the relatively high fire point and low calorific value of esters mean that they will not sustain fire under all transformer fault conditions. No fires have been reported since the use of esters started almost 40 years ago. 


The fire point of ester fluids – which represents the lowest temperature at which the vapour of the fuel will burn for at least five seconds after ignition – is greater than 300°C. This compares with a fire point for mineral oils of 170°C.


A regional fit


Different climates bring different challenges for transformers, and extremes of both hot and cold can pose a failure – and fire – risk. In the Middle East, for example, overheating transformers pose a constant threat to utilities.


One such event occurred in July 2017, when a transformer fire at the Saudi Aramco Mobile Refinery at Yanbu Saudi Arabia was caused by hot weather. On that occasion, the fire was quickly contained, although the extreme regional temperatures mean that the threat of a far more destructive blaze is ever present.


Elsewhere in the Middle East, transformers in Kuwait are designed for an ambient temperature of 58°C – this is the air used to cool the transformer fluid down before it is returned to the transformer. Once back inside, the temperature of the liquid can reach 100°C in a large transformer, or even as high as 130°C in a small transformer – only some 40°C below the fire point for mineral oils. This means that a fault or a hot spot in the transformer would only need to cause a modest increase in temperature to ignite.


With a fire point of more than 300°C, ester fluids provide a much more sizeable buffer between ignition and the ambient air temperature – providing vital protection against fire. Even when inside a transformer in a hot climate, the temperature of ester fluids would have to rise by at least 170°C to ignite, a massive 130°C more than mineral oils. 


A greener, longer-lasting option


Yet the benefits of ester fluids extend beyond minimising fire risk. Unlike mineral oils, they are readily biodegradable and non-toxic. As such, if a transformer is damaged and begins to leak, the chemistry of the esters means it would pose no harm to the environment.


Another vital benefit of esters is that they help to prolong the life of transformers. A high moisture tolerance allows esters to absorb more water than mineral oil. Because esters have a high moisture saturation level, water migrates from the cellulose into the ester, thereby drying the paper in the transformer and reducing the rate at which it degrades. This not only extends the lifetime of the transformer, but also allows it to run at a higher temperature, increasing the available power output. 


Change afoot?


While it is difficult to argue against the high-performance, environmental and fire-safety benefits of ester fluids, the fact remains that the dielectric fluid market is still dominated by mineral oils.

Despite posing a potential fire risk, mineral oils continue to benefit from their own ubiquity. It will take a wholesale change in mentality from a traditionally conservative industry to embrace the alternative.


As the world’s electricity demand continues to rise, and existing transformer fleets grow older, the problem of transformer fire risk is not going away. However, an increased uptake of ester fluids by utilities and transformer OEMs could provide a safe and cost-effective solution.

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