Special Report: Playing with fire

The growing threat of the world’s ageing transformer fleet, by Barry Menzies, managing director MIDEL Dielectric Fluids Global

Barry Menzies, MDS, MIDEL Dielectric Fluids Global.
Barry Menzies, MDS, MIDEL Dielectric Fluids Global.

An underground fire which led to a partial evacuation at Newark Liberty International Airport on January 14 was just one in a series of blazes with a common cause – catastrophic transformer failure.

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 grown, the rate of investment in this critical infrastructure has slowed.

The average cost of a new transformer has risen by 5.5% annually for around 20 years. This has typically resulted in a 100% 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 fires – can occur at any time, but the threat increases as they get older. Industrial transformers have a life expectancy of 20-25 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. But 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 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 end users to minimise fire risk.

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.

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.

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

As the world’s electricity demand rises, and transformer fleets grow older, the problem of transformer fire risk is not going away. But, an increased uptake of ester fluids could provide a safe and cost-effective solution.

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