Study On The Frequency Characteristics Of Audible Noise And Corona Current Of UHVDC Line At High Altitude

With the rapid development of national economy and industry,China’s demand for electricity is also increasing.In order to transfer the high-power power from the remote areas with rich energy to the load areas without power,the state vigorously develops the UHVDC transmission technology.However,with the continuous improvement of voltage level,the electromagnetic environment problems of transmission lines are increasingly serious.Among them,the problem of audible noise caused by corona discharge is particularly prominent,which has been widely concerned and has gradually become an important factor affecting the selection of conductor model.Therefore,the research on audible noise and corona current has an urgent practical significance,and it also has a certain guiding role for UHVDC transmission project,which is conducive to the safe operation and healthy development of UHVDC power grid.Most of the existing studies do not consider the influence of altitude on the electromagnetic environment of UHVDC lines,but the actual UHVDC lines mostly pass through high altitude areas,so it is necessary to study the characteristics of audible noise and corona current of UHVDC lines in high altitude environment.Based on the test section of Tibet Yangbajing UHVDC experimental base of State Grid Corporation of China,the audible noise and corona current of UHVDC line are measured,and the frequency-domain characteristics of audible noise and corona current are studied,and some research results are obtained.Firstly,the frequency differences between the positive and negative sides of the bipolar conductor are compared and analyzed.It is found that the high frequency component of the audible noise spectrum of the positive conductor is significantly larger than that of the negative conductor in the high altitude area.After further statistical analysis of the difference between the high frequency component of the audible noise of the positive and negative conductor,it is found that the difference between the high frequency component of the audible noise of the initial positive and negative conductor increases rapidly with the increase of the voltage after the corona of the conductor When the voltage is in the range of 280 kV～320 kV,the difference between the high frequency components of the audible noise of the positive and negative conductors is basically the same and no longer changes with the increase of the voltage.At each voltage level,the difference between the 20 kHz component of the audible noise of the positive and negative conductors is the largest.Secondly,the difference of A sound level of audible noise between positive and negative leads is compared.It is found that the A sound level of positive lead is larger than that of negative lead,and the difference increases with the increase of voltage.The difference between the theoretical value of audible noise of UHVDC line in high altitude environment and that calculated by traditional BPA empirical formula is also compared,and the reason for the difference is analyzed.The correction value of audible noise considering high altitude factor is obtained,The empirical formula of BPA is improved.Finally,the time-frequency conversion of corona current is realized by FFT.The frequency spectrum of corona current is analyzed,the main energy distribution frequency band of corona current is judged,and the relationship between each frequency band of corona current and audible noise is obtained by multiple linear regression.The results provide a strong support for the further prediction and analysis of the audible noise produced by corona discharge in UHVDC transmission lines at high altitude.