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Vegetable-oil-based electrical fluids will increase transformer safety and minimize environmental impact, according to CWIEME Berlin seminar.

Amid fears of petroleum shortages and increasing environmental pressures, natural esters – commonly known as vegetable oils – have emerged as a renewable, biodegradable alternative to traditional mineral-based transformer oil.
“We have to accept that petroleum reserves are finite,” says Ernesto Ivan Diestre, senior technologist at Repsol, one of the world’s largest integrated global energy companies. “Repsol is seeking a guarantee of a secure supply, with lower emissions and long-term sustainability, thereby contributing to the vision of a more diversified future of energy.”

For the past 10 years the Spanish multinational has been carrying out extensive research into mineral oil alternatives, encompassing both natural and synthetic esters. This research will be the subject of a seminar chaired by Mr. Diestre at this year’s CWIEME Berlin, the world’s largest annual meeting place for the coil winding, insulation and electrical manufacturing communities.
“We tested many different vegetable oils including rapeseed, soya and sunflower and found that those with a high oleic acid content not only matched the oxidation and stability of mineral oils but in some cases even outperformed them,” he says.

Unlike mineral-based dielectric oils, vegetable oils do not form sludge inside the transformer, reducing the risk of electrical arcs. Vegetable oils also help to preserve the cellulose insulation – the most fragile part of a transformer – increasing the service life of the entire device.

Safer, more environmental
The major benefit of vegetable oils as an alternative transformer fluid is that they are biodegradable and non-toxic.
“The industry works hard to avoid oil spills – but accidents do occasionally happen,” says Mr. Diestre. “Vegetable oils would allow us to mitigate any negative environmental impact in that they degrade to carbon dioxide and water in less than 28 days and are not harmful to living organisms.”

This only makes vegetable oils suitable for sealed distribution transformers, however. A viable alternative for power transformers, which are open to the air, has yet to be found.

The other main benefit of vegetable oils is their higher flash point. Mineral oils typically have a flash point of around 150°C whereas vegetable oils have a flash point of around 330°C. This means that the fire risk of a transformer filled with vegetable oil is much lower – an important consideration given their high numbers in urban areas.
“We moved from laboratory to field testing five years ago and so far the behavior of the transformers has been very good. In the coming years I expect to see an increasing co-habitation of mineral and vegetable oils in the transformers around us,” says Mr. Diestre.

Lubricants specialist
Ernesto Ivan Diestre holds a BS in Chemistry from Basque Country University and a BS in Chemical Engineering from Rey Juan Carlos University. Before joining Repsol in 2000, Mr. Diestre spent time at the Gaiker Research Center in Spain and the Anjou Research Center in France. A specialties and lubricants senior technologist, Mr. Diestre dedicates his time to developing new sulfur, petroleum coke, base oil and bio-lubricant products. He has been working in the field of natural-ester-based dielectric fluids since 2004.

His presentation on ‘non-inhibited oil based on natural esters’ at CWIEME Central will take place on Tuesday 24th June, 11:50-12:30.
CWIEME Central seminars are held in English and free for all CWIEME Berlin visitors.

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