Audible Noise From Amorphous Metal and Silicon Steel-Based Transformer Core

Model cores based on amorphous SA1 and HB1 alloys for pole transformers were prepared and their audible noise was measured in terms of A-weighted sound power level in a hemi-anechoic chamber in accordance with ISO 3744 standard. The two amorphous cores annealed under optimum conditions to minimize the audible noise showed the same sound power level of 56 dB as M3 core at their typical operating flux densities. It was found that A-weighted sound power levels increased above 1.4 T for SA1 core and above 1.5 T for HB1 core. This provides design limitations for transformer cores based on amorphous alloys.