Transformers are main components of the Transmission and Distribution system, as it effectively converts high voltage power into lower voltage for the customers of different distribution utilities. Given the critical loads that this equipment handles at a given time, it is important that the transformer is properly designed to withstand specified temperatures and if required, to have overloading capability. Overheating due to overloading could happen in transformers, but this can be addressed by utilizing specific materials in your transformer—in particular, the insulating fluid.
The insulating fluid acts as a coolant and an insulator for the transformers, which means that it is the primary instrument preventing the transformer from malfunctioning due to overheating. Today, transformers are filled with either Mineral Oil-based or Natural Ester-based insulating fluid. Mineral Oil based fluids are derived from petroleum, while Natural Ester fluids are made from vegetable oils. These two serve the same purpose but differ in their properties, more noticeably in their fire safety and sustainability characteristics.
When it comes to fire safety, oil-immersed transformers can have lower fire risk depending on the insulating fluid used. This is where Natural Ester-based insulating fluid comes in, because this fluid base has higher fire point than Mineral Oil. Natural Ester fluid has a Fire Point ranging from 316 to 360°C, [1,2] whereas the fire point of Mineral Oil is half of that at 165 °C.  The fire point by definition, is the lowest temperature at which, once ignited, a liquid in an open container will maintain a vapor pressure sufficient to burn continuously. No known fires have been reported that were caused by transformers filled with Natural Ester fluids. [1,2]
Aside from fire safety, Natural Ester fluids have superior environmental benefits versus Mineral Oil. Made from renewable sources such as vegetable oil, Natural Ester fluids are readily biodegradable, and non-toxic in soil and water.  In contrast, Mineral Oil is not fully biodegradable, and is toxic in water and soil due to the forming of harmful products in soil.  While Mineral Oil contains petroleum, halogens and other compounds, Natural Ester-based oil is free from these, and is also carbon neutral. 
Another advantage of Natural Ester-based oil as a dielectric fluid for transformers is that it can either accommodate higher load capacity, or extend its asset life. Natural Ester fluid has 10 times the water saturation level of Mineral Oil, resulting in an insulating life that is longer than what Mineral Oil offers. Natural Ester fluid can also increase the load capacity of the transformer through its higher thermal capability versus Mineral Oil. This means that the transformer can accommodate higher loads without sacrificing the reliability of the transformer.
With the advantages and benefits of using Natural Ester fluids as transformer insulation, it is no wonder that this makes an ideal option for transformer dielectric fluid, particularly end-users who prioritize environmentally-friendly, cost-effective, and safe solutions for their transformers.
In First Philec, we create value for our customers by delivering these solutions to address their business needs.
 MIDEL Selection Guide: The World’s Leading Brand of Ester Transformer Fluids (2019)
 CARGILL Envirotemp Fluid Data Sheet
 CARGILL Envirotemp FR3 Fluid Brochure
 Mehta, Dhruvesh & Kundu, P. & Chowdhury, A. & Lakhiani, Virendra & Jhala, A.S. (2016). A review on critical evaluation of natural ester vis-a-vis mineral oil insulating liquid for use in transformers: Part 1. IEEE Transactions on Dielectrics and Electrical Insulation. 23. 873-880. 10.1109/TDEI.2015.005370.
 McShane, C. & Corkran, Jerry & Rapp, Kevin & Luksich, John. (2006). Natural Ester Dielectric Fluid Development. 18 - 22. 10.1109/TDC.2006.1668445.