Analysis Of Spectrum Characteristics Of Audible Noise Generated By AC Corona Discharge

With the construction and operation of the ultra-high voltage alternating current(UHVAC)transmission lines,the corona-generated audible noise(AN)has become a significant factor for conductor selection and structural design.Therefore,in-depth investigation of audible noise characteristics is of great engineering significance for the design of high-voltage AC lines.In this thesis,the time-domain measurement method is adopted to obtain time domain waveform of AN and AC voltage.After the analysis of the time and frequency characteristics of the AN,this thesis divides the AN into three parts:impulsive noise,ion-migration noise and background noise.Based on the impulsive,broadband and pure tone characteristic of AN and the voltage periodicity,a noise extraction method using the piezoelectric wavelet transform is proposed.Thus the time-domain waveforms of ion-migration noise and impulsive noise are extracted while the influence of background noise effectively eliminated,which lays a foundation for the analysis of the spectrum characteristics of audible noise.The frequency spectrum of the impulsive noise and ion-migration noise generated by single point discharge are analyzed with different distance respectively and linear correlation between A-weighted sound pressure level and related frequency in the process of impulsive noise propagation is obtained.The propagation characteristics of pure tones of impulsive noise and ion-migration noise are calculated by the point source propagation model.The applicability of the propagation model is verified by the laboratory test data,which provides a new idea for the prediction and analysis of audible noise of AC corona discharge.The source of pure tones of AN generated by conductor discharge are tested and analyzed.The results show that the production of the pure tones generated by conductor discharge has little correlation with the conductor vibration,which is mainly produced by the ion migration movement and the modulation of the alternating voltage to the impulse noise.With the increase of voltage,the contribution of pure tones to sound pressure level is increasing.Based on the process and test results of AC corona discharge,the mechanism of pure tones is analyzed.