Cold Behavior of Dielectric Esters

Natural (NE) and synthetic esters (SE) immersed transformers initially limited to low voltage equipment are becoming more and more diffused in any type of electrical applications (generation, transmission, distribution, industrial) regardless power and voltage. Due to their chemical composition esters exhibit limited performances at low temperatures which must be carefully evaluated in case of application in cold climate countries. Especially in hydraulic generation plant or offshore windfarm, transformers may be taken out-of-service for longer times (days or weeks) and crystallization phenomena may occur. In such cases the measure of pour-point is partially meaningless and “cold and hold” performance must be assessed by testing fluidity after a prolonged standing time at very low temperature.