Apertured electrical coils for sound radiation reduction

Abstract

Industrial coils, such as air-core dry-type reactors, are well known for emitting high-level low-frequency electromagnetic-induced noise. This type of noise generally results from Lorentz forces exciting the coil. In this study, we investigate the effects of introducing apertures into air-core dry-type reactors on the acoustic radiation and associated dynamic behaviors. A simple analytical model of a coil section is first presented to illustrate how porosity, i.e. the aperture size, changes the radiated acoustic pressure. This model shows the variations in pressure inside and outside the coil, as well as the overall dynamic behavior of the most radiating mode in thin shells, i.e. the “ring mode". The transition from solid to apertured structures has interesting dynamical consequences: coupled structural modes detach and change the overall dynamics and acoustics, in ways that are not captured by the simplified model. We investigate these effects through a three-step simulation—electromagnetic, mechanical, and acoustic—which reveals that apertured coils exhibit notably lower acoustic radiation efficiency compared to solid structures, with a reduction of approximately 15 dB at 100 Hz. Thus, our findings offer useful considerations for the design and optimization of apertured coils to decrease acoustic noise generation.