Measurement Methods Study On Noise Radiation Ratio Of Power Capacitor

The noise of power capacitor is the most difficult sources to control in HighVoltage Direct Current (HVDC) substation, which is seriously harmful to the socialenvironment. In order to reduce the noise effectively, it is very important toestimate the noise level of power capacitor correctly. However, different acousticradiation ratios has an direct effect on the acoustic power level of power capacitorradiated. Thus it is significant to research the measurement methods on noiseradiation ratio of power capacitor.To analyze the relation between noise and vibration of capacitor, the structuresteady-state acoustic radiation，sound radiation mechanism of plate structure andthe characteristic of the radiation ratio were studied. Through analyzing the causesof vibration and noise, the propagation path of vibration in the capacitor and thenoise radiation characteristics were discussed. By means of Frequency ResponseFunction(FRF) on vibration and noise，a new formula to calculate radiation index(10lgσ)was deduced.Because of the noise of electromagnetic vibration exciter during theexperiment, a sound insulation cover for the exciter was designed. Then the effectof sound insulation was estimated in a semi-anechoic room. The results testifiedthat the sound insulation is completely meet the requirement, so the noise radiatedfrom the exciter can be neglected during the experiment.Finally, a radiation ratio test system was established in the semi-anechoicroom. To research on the change of radiation index with frequency under differentmeasurement methods, and verify the accuracy of radiation index in mainfrequency, sine sweep signal, white noise and sine monophonic wave were used toexcite different surfaces of the capacitor. The results showed that the more reliablemeasurement method of Radiation Ratio is sine sweep signal in laboratory. Andradiation ratio cure was changed along with frequency, it’s different much from theconstant.Through researching on measurement methods of noise radiation ratio forpower capacitor, on the one hand, it can provide a reference for normalizing theexcite signal of radiation ration in the laboratory, on the other hand, it can get thenoise radiation ratio of a certain type capacitor.