| In recent years,China’s electricity demand has grown rapidly.However,the distribution of energy centers and load centers in China is unbalanced.Therefore,it is necessary to vigorously develop large-capacity and long-distance transmission systems.In order to save line corridors,experts and scholars have proposed a new transmission method of AC and DC lines erected on the same tower.In order to solve the electromagnetic environment issues of AC/DC transmission lines under high humidity,high altitude,and haze conditions,it is planned to build an artificial climate chamber that can regulate environmental conditions such as air pressure and humidity,and can simultaneously lead in AC and DC voltages.Wall bushings are usually used to lead high voltage into the climate chamber,but due to the compact structure of the climate chamber,AC and DC wall bushings can only be placed parallel and and the distance between the two is relatively close.According to the simulation results of the electric field,the end of the high-voltage guide rod of the wall bushing is the area most prone to discharge.In order to prevent discharge of the wall bushing during the experiment and affect the accuracy of the experiment,it is necessary to study the corona discharge characteristics of the highvoltage guide rod.Firstly,a scaled electrode for high-voltage guide rods and an experimental platform for corona inception of high-voltage guide rods under AC/DC combined voltage are designed in this article.The platform is composed of a low potential four channel synchronous acquisition system which is used to capture corona pulse signals,and a digital filtering which can determine the corona inception time and obtain the corona inception voltage.The maximum surface electric field strength is calculated by a three-dimensional high-voltage guide rod scaled electrode model.Secondly,by changing the proportion of AC voltage in AC/DC combined voltage,electrode radius,distance between electrodes,environmental humidity,and DC voltage polarity,the changes in the corona inception voltage and maximum surface field strength of the guide rod under AC/DC combined voltage are explored.The experimental results show that by increasing the proportion of AC voltage,the DC voltage component decreases linearly.Meanwhile,as the proportion of AC voltage increases,the maximum nominal field strength on the surface of the guide rod increases.Increasing the electrode radius on the DC side,the DC voltage component increases at the same AC voltage.At the same time,as the radius increases,the maximum nominal field strength on the surface decreases,and the slope of the field strength changes with AC voltage decreases.Increasing the distance between the guide rods increases the DC voltage at the same AC voltage,and the absolute slope of the DC voltage with the change of AC voltage decreases.However,the maximum nominal field strength on the surface hardly changes with the distance between the guide rods.Increasing environmental humidity results in a decrease in both DC voltage and maximum field strength under the same AC voltage,and the degree of reduction is greater at higher humidity.In addition,under the same geometric and environmental conditions,the negative DC-AC corona inception voltage is greater than the positive DC-AC corona inception voltage.Finally,a two-dimensional fluid model is established in this article to explore the corona inception characteristics of the high-voltage guide rod.The simulation results show the motion and concentration changes of particles during the corona inception process,field strength attenuation process,and field strength recovery process under equivalent positive corona and equivalent negative corona.The simulation results show that after the equivalent positive and negative corona ends,the main remaining ions in the space are positive and negative ions.Due to the different mechanisms of equivalent positive and negative corona generation,positive ions have a stronger inhibitory effect on equivalent positive corona from a quantitative perspective,while negative ions have a stronger inhibitory effect on equivalent negative corona from a distance perspective.By comparing the synthesized field strength under two different conditions,it is found that the inhibitory effect of negative ions on the electrode surface field strength under equivalent negative corona is more significant than that of positive ions on the field strength under equivalent positive corona,thus verifying the experimental conclusion:the negative DC-AC corona inception voltage is greater than the positive DC-AC corona inception voltage. |
