Twenty years of data shows how this natural ester enhances the insulation of electricity transformers.
During the past two decades, vegetable oil has helped transform electrical transformers, with extensive research highlighting its ability to enhance the efficiency and longevity of transformers.
Engineers at Essential Energy have been at the forefront of gathering the data that shows the oil, traditionally known for its culinary uses, is a highly effective insulator for electricity transformers.
By providing environmentally safe insulation, vegetable oil also improves the performance of these critical components and contributes to a more sustainable energy infrastructure.
Essential Energy installed the first electrical zone substation transformers filled with vegetable oil adjacent to National Parks in New South Wales in 2005. Further innovative applications, such as the potential for ester-filled distribution transformers at electric vehicle (EV) charging points at fast-charging stations, underscore the safety and versatility of vegetable oil well beyond the kitchen.
Out of the fryer: a brief history
In the 1990s, the initial venture was to use plant-based oils in small pole-top transformers to minimise the impact of a spill. The breakthrough was to use food-grade antioxidants to prevent the vegetable oil from becoming rancid. Chemical additives were also used to improve the thermal properties of vegetable oil.
As the industry became more confident, these fluids were used in larger power transformers, such as those in power plants and substations which provide a step up or down in voltage to enable the safe transmission of electricity over long distances.
In Australia, Essential Energy commissioned research and development on the use of insulative properties of natural esters in power transformers in 2004. These power transformers were among the first to use natural esters as an alternative to mineral oil worldwide.
Essential Energy Substation Engineering Manager, Lindsay McPherson, said, “We began using vegetable oil to insulate transformers adjacent to the National Parks where we could reduce the environmental risk of leaks.
“In 2007, we joined with Monash University and Ausgrid to do research and development on further uses of vegetable oil in the business.
“Now, we have 22 power transformers up to 132kV, each containing about 10,000L of vegetable oil along the borders of the National Parks, with more at other sites in our network.
“Our transformers weigh at least tens of tonnes, as 10,000 litres is ten tonnes, and then you have all the metal on top, so there is a lot of engineering behind the scenes.”
The data on vegetable oil
Data on the condition of the transformers has been collected during the past 20 years, with oxidation being the primary concern when using vegetable oil. Oxidation leads to the formation of acids, sludge, and other by-products that degrade the oil’s insulating properties and may compromise the transformer’s performance and lifespan.
Armed with research from regular tests for acidity, oxidisation and moisture exposure, data has shown that natural esters – such as vegetable oil – are a great alternative to mineral oil in applications where fire risk or environmental sensitivity are of concern.
Fellow Essential Energy engineer and innovator, Daniel Martin, said they have been looking for any changes in the chemical measurements, and so far, all the data has remained well within standards, even during faults and extreme temperatures.
“While natural esters are known to have lower oxidative stability than mineral oil, the data strongly indicates that vegetable oil is effective as insulation over the long term, as long as the tank is sealed.
Mr Martin said testing has not indicated a long-term degradation of the oil, nor has there been a reduction in the cyclic rating or operation of the transformer.
“Now that the transformers are entering their 20th year, the data gives us the confidence they will last another 20 to 30 years, at least. The units have operated without incident and are enabling learning about the long-term in-service performance of natural esters.”
The big unknown has been the longevity of the transformers, and even manufacturers can’t say how long vegetable oil could be used. Where there have been faults, the fluid inside has remained as good as the day it was filled.
“We expect at least 60 years of life for these transformers, given they typically have a lifespan of 25 to 40 years.
“This range varies based on factors such as the quality of manufacturing, operating conditions and maintenance, as well as ambient temperature, load levels, and environmental conditions which also play significant roles in determining their longevity,” said Mr Martin.
Natural esters also have a fire point of 360°C, compared to that of mineral oil at 180°C, which means they are safer to install near buildings and sites with an environmental risk. This provides a safety aspect that has allowed Essential Energy to install transformers next to a heritage site in Wagga Wagga, with further transformers to be installed near an irrigation canal at Yenda, a switch room in Lismore and next to a service station in West Bathurst.
The benefits and beyond
Two affable transformers named Kermit and Jaffa also play a significant role in this story. The green one (Kermit) and an orange one (Jaffa) are also known as ‘strategic spares’ and can be transported for use as a backup in the event of a transformer failure, where the wait time for a replacement can be as much as 60 weeks.
Such is the case at Bathurst, where Kermit was called into action next to a service station and filled with vegetable oil, which provides a higher level of safety and power supply until a permanent transformer arrives.
Essential Energy Senior Engineer, Sam Mulquiney, said transformers like Kermit and Jaffa provide significant cost and time savings.
“Kermit and Jaffa are great for emergency response as they are compact units.
“The ester fluid provides a quick response to a network event by allowing us to transport a fully assembled transformer, and it reduces our environmental impact in the event of a fluid spill during transit.”
Mr Mulquiney said the ester fluid also allows for the transformers to be installed as a temporary measure across the majority of Essential Energy’s network substations, including environmentally sensitive sites such as national parks.
“Ester fluid provides benefit from a fire risk when replacing transformers in existing substations where transformers are near buildings. The enhanced fire properties negate the need to build fireproof walls, which provides a significant cost saving.”
Essential Energy Manager of Innovation, Brad Trethewey, is working with RACE 2030 and the University of New South Wales to understand the thermal behaviour of ester-filled transformers at EV fast charging points.
He said this presents challenges and benefits to a distribution network where significant investment in upgrading or installing transformers to meet the load of EV chargers may be required.
“Most utilities use the nameplate rating of transformers to determine the available load on the asset and if there is a need to upgrade,” Mr Trethewey said.
“We are seeking to understand the impacts on the temperature range that transformer windings will need to tolerate.
“This will, in turn, improve our understanding of a transformer’s thermal behaviour during EV fast charging sessions with the goal of reducing the need to invest.”
The transformation continues
Mr Martin has been comparing and discussing new findings by liaising with other utilities via the various engineering society events held with the Electric Energy Society of Australia (EESA), the Institute of Electrical and Electronics Engineers (IEEE) and Engineering New Zealand. He is also on Standards Australia advisory panels which look to keep industry know-how up to date.
Mr Martin, Mr McPherson and Mr Mulquiney are also collaborating with industry through CIGRE (International Council on Large Electric Systems), which brings together like-minds to gather industry-led research that generates further innovations.
While the use of vegetable oil has the potential to significantly reduce the environmental impact on the ecosystem, ester-filled transformer units must be properly sealed to prevent oxygen and moisture from interacting with the oil. However, Essential Energy’s studies have shown that this can be managed over several decades.
With ongoing research and innovation, vegetable oil continues to pave the way for a more sustainable future in electrical transformer technology. It also just happens to add crunch to a well-cooked potato chip.
