Why retrofill? Transformer safety and high-rise buildings. By Barry Menzies
From a 48-storey fire in the UAE, to a 200-firefighter-strong blaze at student accommodation in the UK, several high-profile, high-rise fires continue to keep the focus of utilities, regulators, developers, and public associations everywhere on actively seeking ways to reduce the risk of fire with innovative materials.
Statistics show that the majority of fire related fatalities occur in a domestic setting between the hours of 10pm and 6am. Protecting high-rise residential buildings from fire, where occupancy rates are high but the reaction to danger is lower (while asleep), is a critical engineering challenge.
While most recently built high-rise buildings will be equipped with risk safety provisions such as wet or dry risers, protected staircases, sprinklers, and communications systems as standard, thousands of post-war, purpose-built flats require careful risk assessment and improvement. What was acceptable at the time of build may no longer meet today’s standards or may have been affected by changing environmental factors such as the encroachment of neighbouring buildings. While the fire safety legislation adopted in 2006 has driven improvements that seek to address these types of issues, its application has sometimes been problematic, with varied results from site to site.
A fire risk assessment is the first step in evaluating the risks posed and identifying options to reduce the potential for a devastating event. Electricity substations, which are often located in the basement or adjoining a high-rise building, will often be identified as a potential fire risk due to the proximity of a source of a fuel – mineral oil – to a source of heat and sparks. This concurs with the findings of the MIDEL Transformer Risk Report 2020, where respondents identified fire risk as the second most important consideration when assessing transformer risk overall.
Mineral oil is widely accepted as the most flammable of the insulating fluids used within a substation’s transformers, but has persisted in its use due to its price point. A mineral oil fire will burn ferociously, producing thick, black smoke, impeding evacuation by reducing visibility and potentially jeopardising ground floor and basement exits. At their worst, there are documented cases where transformer fires have caused loss of life and significant damage to the environment. They are certainly not a risk to be ignored.
In newer buildings, the use of mineral oil in a transformer needs to account for the substation to be constructed to the latest fire safety standard – reinforced concrete or brickwork with a minimum four-hour fire containment rating. In addition to fire suppression systems involving significant civil engineering works, these measures do not eliminate the risk of fire by preventing it but are necessary to contain a fire once one starts. Additionally, in older buildings, where the retrofitting of concrete reinforcements or a complete relocation of the substation would be expensive and technically challenging (if not impossible), the fire risk can be mitigated in a completely different way once mineral oil is eliminated from the equation.
One pioneering UK utility is leading the way in mitigating transformer-related fire risk. Following the fire at Grenfell in the UK, the utility considered that any element of risk was no longer acceptable and so undertook a sizeable and substantial review of its property portfolio. It subsequently identified over 100 residential sites where upgrades could be made to further enhance fire safety and the safety of residents. Many of these higher-risk units are located in embedded substations in the basements of the high-rise apartments that rely on them for electricity. The units range from 500kVa to 1000kVa.
After exploring the options, the utility embarked on an extensive programme of corrective upgrades at a scale never seen before in the UK. One long-term and economic solution to reduce transformer fire risk stood out; replace the mineral oil in each transformer with a fire safe alternative. Synthetic ester fluids are a K-class rated fire-safe and biodegradable alternative to mineral oil, and it is increasingly being chosen by power utilities and end users to minimise fire risk.
The contract for the utility’s schedule of upgrades was awarded to MIDEL Service Partner Grosvenor Oil Services who opted to use MIDEL 7131, a synthetic ester transformer fluid, that has a high fire point of 316°C, far exceeding that of mineral oil (180°C). The significantly higher fire point makes it the ideal choice for improving the safety of transformers located in residential and high-rise buildings. The retrofilling technicians leveraged their experience of MIDEL’s ester liquids to the benefit of the project – and the safety of residents. For each site, the technicians inspected the condition of the transformer before draining it of the mineral oil and flushing it through. Once completed, the transformers were retrofilled with the fire safe synthetic ester and tested.
Replacing mineral oil has several benefits beyond the peace of mind it brings to residents in high-rise buildings. For one, it significantly enhances the sustainability of substations: ester fluids are biodegradable and non-toxic – in the event of a leak, it does not pose a threat to the environment or to people that 9come into contact with it.
Ester fluids also keep the transformer in better condition for longer, by reducing the impact that water ingress has on components such as the insulating paper. Because of this benefit, ester-filled transformers require less frequent quality testing (once every five years, rather than once every 12 months). Subsequently, this reduces utilities’ maintenance burden as well as increase uptime. Sites are also better protected against unexpected power outages due to failure. Finally, it offers the ability to safely increase transformer load, a benefit that became particularly fortuitous when the Covid-19 lockdown significantly increased domestic property electricity demand.
While pioneering, this utility is not alone in its efforts. Utilities across the UK are turning to the benefits of fire-safe materials to reduce the potential for transformer fires in high-rise buildings and higher-risk locations such as hospitals, schools, and shopping centres. The benefits and the process of retrofilling is well-established, and with many more people expected to work from home for the foreseeable future, there is not a moment to waste to ensure that the thousands of transformers that supply domestic power are fire safe, sustainable and reliable.
Barry Menzies is Managing Director at MIDEL, the world’s leading brand of ester transformer fluids. Since the 1970s, MIDEL transformer fluids have been chosen by utilities and transformer manufacturers across the globe. MIDEL synthetic and natural ester fluids are acknowledged for their excellent fire safety and environmental protection properties, driving installation savings as well as mitigating transformer fire risk.
For more information, please see: www.midel.com