TRANSFORMER DESIGN OPTIMISING TRANSFORMER DESIGNS WITH NATURAL ESTERS Transformers utilising a standardised high temperature capability can increase reliability and loading capability by up to 20% while reducing the amount of materials and fluid required to create smaller, more effective transformer designs. C ellulose paper, pressboard, and dielectric fluid typically comprise a transformer’s insulation system. A common failure mode of an electrical transformer is caused by the degradation of the solid insulating system (cellulose paper). Subsequently, the (temperature) operating limits of a transformer are constrained by the thermal capabilities of the insulating materials within each design. However, that changed with the validation of enhanced insulation system life and high temperature capability enabled by natural ester dielectric fluids. PROTECTING THE TRANSFORMER INSULATION SYSTEM One of most significant factors contributing to the insulation system aging rate is moisture. In the insulation system, the relative water saturation level of each component will move towards equilibrium. Typically, in new transformers, this means water should leave the solid insulation and be absorbed by the fluid. One of the by-products of paper aging due to thermal breakdown is the emission of H 2 O (water) molecules, which makes the system ‘wetter’. Thermal breakdown (and aging) subsequently accelerates in a wet system, and the cycle continues; this autocatalytic reaction creates an exponential aging rate. Mineral oil is very limited by its chemical structure to absorb this moisture. At 20 O C, mineral oil is fully saturated with 65 parts per million (ppm) of water in solution. This limitation forces most of the water to stay in the cellulose. This trapped water destroys the cellulose bonds, thus weakening the insulation system. SOLID INSULATION IS MUCH ‘DRIER’ Thermal aging cannot be avoided or stopped, but it can be slowed. Natural esters, like FR3™ dielectric fluid, perform very differently in the same scenario. First, the chemistry of FR3 fluid enables it to absorb a much greater level of water before reaching saturation (approximately 1000 ppm of water); therefore the solid insulation is much ‘drier’ than a comparative mineral oil system. Second, operating transformers reach temperatures that enable hydrolysis to occur: H 2 O molecules are ‘consumed’ by FR3 fluid, yielding long-chain fatty acids. The result is a reduction in the water content of the FR3 TM natural ester fluid vs mineral oil. Sealed tube test – ML 152-2000 42 Aquatic toxicity test fluid, maintaining its relative dryness. Those long chain fatty acids then react (bond) with vulnerable sites on the cellulose in a process called transesterification (taking up space where water would normally reside and cause damage to the cellulose). The comparative results of aging studies are striking. As a mineral oil system ages and generates more water, it causes the system to age more quickly in a degenerative process. An FR3 fluid system is relatively ‘drier’ as the water it generates is consumed; the result is a much slower aging process when operated at the same temperature as systems containing mineral oil. Evaluated using industry standard accelerated aging test methods, an FR3 fluid system operating at conventional temperature limits lasts five to eight times longer than the equivalent mineral oil system. WHAT IS FR3 FLUID? FR3 fluid is a natural ester derived from renewable vegetable oils. It provides improved fire safety, transformer life/ loadability, and environmental benefits greater than those of mineral oil. ESI AFRICA ISSUE 4 2014