Sound isolation of large transformers mounted on raised floors

Abstract

Transformers for substation service mounted on elevated floors often cause spurious sound to be transmitted to the spaces below it. Magnetostriction vibration of the massive iron core at 120 Hz and its harmonics drives the supporting floor to emit sound into the spaces below. Contemporary vibration isolation design fails to prescribe the proper isolation method since the mass of that transformer considerably exceeds that of the participating mass of the concrete floor. A vibration isolation paradigm is proposed of a two-body system in inertial space; the participating mass of the concrete floor being the second active body; the virtual mass of the pair along with the spring stiffness determines the resonance frequency. The ratio of that resonant frequency to that to be isolated is a measure of the expected isolation. For good isolation, the resonant frequency should be 1/10th that of the vibration to be isolated. The floor participating mass is approximated as a square one-half wavelength of the thin conc...