With fast development of high-voltage DC（ HVDC） transmission system

a large amount of noise is radiated from the ac filter capacitors of converter stations and it is significant to study the propagation law of capacitor audible noise. In this paper

the test platform for the study of capacitor noise characteristics is established. The noise levels radiated from the tested capacitor are measured at several distances and different currents under each frequency

the variation relation of radiation noise of capacitor with distance is analyzed and the propagation mode of capacitor noise is identified based on the theory of sound propagation. It is shown by the result that

in the measurement range of this paper

the radiation of noise from the bottom and top surfaces is obviously a spherical wave mode

whereas the radiation of noise at side is cylindrical wave mode at near distance and is spherical wave mode at remote distance. The total noise level decreases 5. 4 dB as the measurement distance doubled

indicating that the total radiation noise of capacitors propagates closely in the form spherical wave mode.