Practical Experience of Natural Esters Quality Maintenance

Nowadays, the environmental requirements in the electrical industry have increased. Natural Esters are one of the alternatives to replace mineral oils in power and distribution transformers due to their high biodegradability and environmental clearness in general. This paper explains the differences in processing natural ester fluids as compared to processing regular mineral oils. The experimental work involves the use of single and double-stage vacuum degassing systems applied for natural esters processing for power transformers. A series of oil analysis methods including but not limited to: dielectric strength, total dissolved gasses, and water content were measured to classify service-aged natural ester fluids. As it is recommended by IEEE Std. C57.147, two methods can be applied to recondition natural ester oil: mechanical (vacuum dehydrator) and chemical and adsorbent (oil regeneration plant). Before the filling and during the operation process, the natural ester dielectric fluid must be serviced. Natural esters have lower gassing tendency as compared to mineral oils. The chemistry of esters is significantly different from petroleum-based oils and requires a different approach for processing. The results showed that high and low vacuum dehydration systems are is efficient not only for mineral oils but also for natural ester oils. The interface to operate the system considers temperature control and other parameters to recondition vegetable-based transformer oils to the “like new” condition.