Sound Power Measurements in the Near Field of Transformers

Abstract

The international standard for the determination of the sound power level of transformers allows both the sound pressure and the sound intensity measurement method. Since the sound measurements take place in the reactive near-field next to the vibrating transformer tank walls, local disturbances influence the sound field characteristics at the measurement positions. As a result, the measured mean sound power level differs commonly up to 6dB at comparative measurements with both methods. Beyond these near field effects, the influence of an industrial measurement environment (background sound sources, hard-reflecting floor, semi-reverberant walls, and standing waves) to the sound pressure and sound intensity field characteristics is investigated. Hereby, numerical analyses based on 3D-FEM with consideration of the fluid-structure-coupling are used. The measured sound level differences can be re-produced and clarified in numerical analyses.