Dielectric Ester Transformer Fluids: Extending the Life of Insulation

Published under Technical Articles

Insulation deterioration is a leading cause of transformer failures. Over its lifetime, it will degrade when subject to high temperatures. The insulation paper is commonly made of cellulose. A byproduct of cellulose degradation is a higher water content in the oil. There is some evidence showing that the water that is present in the cellulose will auto-accelerate the aging in oil. If the water is able to be wicked from the cellulose, it will slow the aging. The acceptable saturation of water in FR3 when compared mineral oil is close to fifty times higher. Due to this, it is encouraged to store FR3 under a nitrogen blanket and avoid any unnecessary exposure to humidity in the atmosphere. However this means FR3 is able to wick away more moisture from degrading insulation paper, which in turn will decelerate the aging process. It is claimed that it can extend the insulation life by 5-8 times the amount that is normal with mineral oil. The above figure shows the comparison under similar temperatures in FR3 compared to mineral oil. Usually transformers are rated for 55 degree rise to minimize the aging of the insulation under normal conditions. If the load on the transformer is increased, the temperature will rise. In mineral oil, this can cause a much more rapid degradation; however, FR3 is able to counteract this aging. Transformers filled with FR3 can be loaded more without negative effects. Smaller footprints can in turn be engineered with the higher loads. There are typically three options that can be chosen from when engineering a transformer filled with FR3. First, you can load the transformer the same as one with mineral oil. This will result in an insulation lifespan of 5-8 times the length of its counterpart. The second being a slightly higher load. The temperature will be increased, which won’t prolong the insulation life as much as a the less-loaded option, but it will incrementally increase the lifespan in comparison to mineral oil. The last option is a higher load on the transformer with a lifespan equal to a transformer with mineral oil. Cargill claims that a transformer can be loaded 20% more than its mineral oil counterpart with the same lifespan. With this flexibility, you can use FR3 to meet your specific load requirements, while still staying within other project constraints. If you are interested in learning more or want to find a transformer that contains these fluids, don’t hesitate to contact us. Keep UTB in mind and we can help you source your next transformer. _________________________________________________________________________________

Quinn Alleman

Utility Transformer Brokers


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