In order to measure the noise of the ac filter capacitor accurately and reduce the requirement of the test power source and other equipment in the condition of accurately measurement. This paper is based on the noise test of filter capacitor in Changji—Guquan ± 1 100 kV HVDC project. For the four types of capacitor products

the bridge circuit is used to load the full harmonic current specified by Changji—Guquan ± 1 100 kV HVDC project the noise test is carried out under the conditions of the former three main currents and the proportion reduce of the full harmonic currents; and the sound pressure level and the sound power level of the capacitor under the corresponding conditions are obtained. The test dates show that when the high harmonic currents amplitude exist the gap on the main three current amplitude

use the three main currents as the condition of injection

the sound power level deviate within 0. 4 dB. When the harmonic current of higher harmonic current amplitude and other currents amplitude does not exist the gap on the order of magnitude

use the proportion reduce of the full harmonic currents to do the test

and then calculate dates under 100% full harmonic noise sound level by formula. The test data show that the formula can be used under more than 40% harmonic current

the sound power level deviate within 0. 1 dB.