Long-term reliability of iron-based amorphous alloy cores for oil-immersed transformers

Long-term property reliability was examined for iron-based amorphous alloy for use in oil-immersed transformer cores. The core loss changes of amorphous cores under accelerated aging in air and insulating oil were traced. In addition, the causes of the property deterioration were analyzed. It was found that iron-based amorphous alloy was not crystallized by aging at 200°C for 17 months. When aged in air, magnetic properties deteriorated because of oxidation of the surface before crystallization. Insulating oil by itself did not accelerate the deterioration of magnetic properties. When aged in insulating oil with insulating papers, moisture was formed on the surface of the amorphous alloy, causing property deterioration. In application as an oil-immersed power transformer core operated below 105°C, core less increase would be less than 10% during a 30-year practical lifetime. Thus, the amorphous alloy seemed to have enough reliability for the core material