Study Of Characteristic Of Audible Noise From The UHVDC Line In Corona Cage

As one of the important parameters of electromagnetic environment of UHVDC transmission line, audible noise produced by corona discharge is an issue that must be considered in design. At present, our country has carried out some research of audible noise in view of the engineering demand, but the study about spectrum characteristic of audible noise under different conditions and the calculation of inception voltage when some attachments on the surface of conductors is less. Also in order to provide some reference to the actual engineering, we discusse the influence of structure parameters of transmission lines on the ground audible noise.In the thesis, we study the spectrum characteristic of audible noise from the UHVDC transmission lines in a large outdoor corona cage. The results show that the effects of background noise on audible noise mainly in the low frequency part; the audible noise of positive pole is bigger than the negative pole, we can apart the audible noise of positive pole from the background noise after 1.25kHz,while it will be 2.5kHz for the negative pole; the spectrum characteristics of audible noise are basically the same for the both side of bipolar and they are similar with the characteristic of positive pole; rain and snow both affect the audible noise, the value after rain or snowing is slightly big than before within 630～8kHz range of frequencies.The influence of water drops attached to the surface of smooth conductor on the inception votage was also studied in this thesis. The study shows that the inception voltage is higer when there is no water drops on the surface of smooth conductor, and it decreases obviously when there s water drops on the surface; it decreases gradually with the increase of suspended water volume; with the increase of the water drop relative dielectric constant, it decreases gradually and the decrease rate tends to small; the shap of water drop also has influence on the inception voltage, the top of the water drop is sharp, the voltage is the lower.Audible noise empirical formulae of DC line from different institutions are evaluated and analyzed at last, we conclude that the EPRI formula is better suitable for predicting the audible noise of UHVDC transmission lines in our country with the comparison of the measured data belonged to the actual engineering. Then we analyze the effects of different lines structures on the ground audible noise based on the formula, it has certain guiding significance to the design of UHVDC transmission lines in China.