Transformer design and manufacturing for natural ester fluids
One of the most important and expensive equipment in a transmission and distribution network is a transformer. The main function of a transformer is to transform the energy and power at the most economical voltage, where the proper electrical and thermal design of the transformer is of great importance. Transformers are filled with fluids for dielectric and thermal purposes. Petroleum-based oil has been used as a fluid for fulfilling the dielectric and thermal requirement for over 100 years. Petroleum-based oil (mineral oil) is not a biodegradable fluid, and this has led to the development of environmentally friendly ester insulating fluid for electrical power applications. The high fire point of ester fluid reduces the risk for transformers installed close to a building or people or even for indoor applications. Though biodegradable and fire-resistant, ester has a higher viscosity than mineral oil, which is a challenge for the transformer designer and manufacturers.
VTC/GTC team has successfully designed and tested a 150 MVA transformer insulated with natural ester Envirotemp™ FR3™ fluid, one of the largest FR3 insulated transformers built in the USA. Our team has built and tested units up to 750 kVp Basic Insulation Level. Envirotemp™ FR3™ is a product of Cargill.
VTC/GTC team has successfully designed and tested a 150 MVA transformer insulated with natural ester Envirotemp™ FR3™ fluid, one of the largest FR3 insulated transformers built in the USA
Properties of natural esters
Virginia Transformer has developed Envirotemp™ FR3™ ester-filled transformers for biodegradable applications as well as for indoor applications based on customer requirements. Ester FR3 is a fire-resistant fluid created from edible seed oil and food-grade performance-enhancing additives. It does not contain any petroleum, halogens or silicones. It is tinted green in colour, and a has fire point of 360 °C and flash point of 330 °C. Natural esters can hold a higher amount of water than mineral oil. Due to this property, the water content in newly received oil can be 200 mg/kg as per IEEE. Table 2 of the standard  provides acceptable values for ester fluids. The moisture is bonded to the oil molecule and does not affect the insulation. Also, the power factor of 1 % in ester is equivalent to 0.5 % in mineral oil. The viscosity of the fluid is 4 times that of mineral oil for the operating temperature of 80 °C, shown in Fig. 1.
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