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Biodegradable ester oil for transformers?

A high-voltage transformer in the main grid may contain as much as 100 tonnes of mineral oil, which is used as an electrical insulator and cooling medium. The environmental risks associated with transformer oils are very unlikely to be realised, but it is still necessary to make contingencies for them.

Fingrid’s environmental specialist, Jenni-Julia Saikkonen, knows how non-toxic, biodegradable ester oils could be used instead of mineral oil to affect the management of the environmental risks associated with high-voltage transformers.

“The biggest risk associated with transformers is the risk of fire. If there were a fire, the heat, smoke, and any oil leaking from the transformer, along with the oily fire extinguishing water, would constitute a risk to the environment, safety, and electricity transmission,” Saikkonen says.

However, she points out that transformer fires are extremely rare; the last one to occur in Finland was in the 1980s.

Saikkonen appreciates the many favourable properties of ester oils. One of the most important is that the flash point of ester oil is higher than that of mineral oil.

“In practice, ester oil is non-combustible.”

Consequently, when ester oils are used in transformers, the clearances required for fire safety can be much smaller, and there is no need to implement protective walls or fire extinguishing systems in case of a transformer fire. The shielding pool, which is necessary to contain leaking oil and fire extinguishing water, could also be smaller.

Ester oil may also extend the transformer’s service life, and it would be possible to place loads on the transformer at a higher power level.

There are also challenges to tackle: Natural ester oils made from renewable raw materials are at least nearly carbon neutral.

Natural ester oil solidifies in cold air, limiting its usefulness. Synthetic esters manufactured from petrochemical by-products do not suffer from the same solidification problem.

Ester oils are also somewhat more expensive than conventional transformer oils, but the price difference has levelled off in recent years.

“Ester oil has been used in equipment operating at a lower voltage level, but around the world, it has seen little use in high-voltage equipment. Pioneering work is needed in this field, and Fingrid is ordering the first device insulated with ester oil for a substation located in a groundwater area.”


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