This paper deals with EDF Research and Development work for ERDF needs in terms of energy efficiency, focused on Amorphous Metal Distribution Transformers (AMDT). Many prototypes built on METGLAS® 2605SA1, rated 250 to 630 kVA from different manufacturers, were tested under short-circuit conditions according to IEC and ERDF standards. Some of the prototypes exceeded the accepted value of 4% of impedance variation after short-circuit. Rectangular windings offer poor resistance to short-circuit stresses. Small metal particles, detached from amorphous core, were found at the bottom of the tank. In that case, dielectric strength is not gifted. The results show the active part should be strong enough to support high electrodynamic forces produced during short-circuit test.

To evaluate the physicochemical compatibility of rapidly solidified ribbons with transformer insulating fluids, isothermal heating process was carried out in order to prove the sustainability of these materials. Fe-based amorphous ribbons were immersed in mineral and vegetable transformer oils for a period of 580 hours at 110 and 140°C. Chemical analyses of oils after experimentation have shown absence of amorphous alloys' components such as Fe, Si and B. In addition, a stability of magnetic properties is witnessed via the measurements of iron losses. Moreover, X-ray diffraction patterns of ribbons after aging experiments reveal a fully amorphous structure. Calculated lifetimes from accelerated aging test show a good stability of amorphous ribbons in field conditions.

International audienceThe microstructure and the solute distribution inside the phases after isothermal holding in the temperature range between 420°C and 700°C in the Ti-5553 alloy were analyzed using TEM equipped with an EDX analyzer and atom probe tomography. When phase transformation occurred at high temperatures (≥ 600°C), a significant partitioning of all solute elements was characterized. After a long holding time, the distribution was nearly homogeneous in each phase. For a transformation at lower temperature (410°C), a low partitioning was observed at the beginning of the transformation, after 40 min, and the precipitates composition notably evolved with increasing time toward an expected composition of equilibrium alpha phase

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