In this paper

the noise of AC filter capacitor unit for ±800kV UHVDC project under construction or to be operated in China is measured through the noise measurement system which is set up on the basis of microphone

the relation between harmonic current and the noise of capacitor unit is studied.The noise reduction measures for the capacitor unit is proposed and adopted to verify the noise reduction result. It is shown by the study result that since the 11 th and 13 th harmonic current is too big the noise level of BP11/13 filter capacitor unit reaches above 65 dB. And the total noise reduction level can be reduced above 5 dB after the addition of such external noise reduction measures as sound-absorbing enclosures