Transformadores elétricos com núcleo de liga amorfa para aplicação em aeronaves

Abstract

In order to reduce the mass of eletrical transformers and generators in aircrafts, many manufacturers have adopted 400 Hz as the operation of these devices. However this frequency causes increased core losses which were disregarded due to the small involved powers and non continuous basis operations. By considering similar sizes, newer aircraft models are more electricity dependent and the generated power increased from 240 kVA to 1000 kVA. In this new scenario losses cannot be neglected and other options for increased efficiency should be considered. Iron-based amorphous transformer cores AEFture reduction by up to 70% loss while operating in 50- 60 Hz. However smaller magnetic saturation induction values result in higher weight than similar cores made of crystalline Fe-Si, therefore, undesirable in aircraft. This work discusses that, when particularities of aeronautical transformers are considered, one can design a power transformer with an amorphous core with smaller mass and losses than a similar with a Fe-Si crystalline based core. For this purpose, a hand-made amorphous core transformer was built to operate at 400 Hz, which has been thermo-magnetically treated to enhance its electromagnetic properties. Through electrical test, equivalent circuits of transformer were obtained for both core conditions: unannealed and annealed. Comparisons of masses and losses between an aircraft transformer with crystalline core and the hand-made amorphous one show that the latter has lower losses and that, when obeyed the particularities for aeronautical transformers, they may have smaller masses. Details and explanations about the thermomagnetic treatment, evidencing by X-ray diffraction of no-crystallization, after core heat-treatment and hand-made transformer evaluation through simulation are also included in this work.