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.
Cellulose paper, press board, 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 H2O (water) molecules, which makes the system ‘wetter’. Thermal breakdown (and aging) subsequently accelerates in a wet system, and the cycle continues; this auto catalytic reaction creates an exponential aging rate. Mineral oil is very limited by its chemical structure to absorb this moisture. At 20OC, 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.