| With the development of power grids,UHV DC transmission plays an important role in strengthening inter-provincial power grids and exploring flexible interconnection between large power grids.However,the terrain along the UHVDC transmission is complex,the transmission lines in the mountainous area are vulnerable to lightning strikes,and the lightning protection design of UHVDC transmission lines is mainly based on the experience of low-voltage-rated line operation.In order to find the optimal configuration relationship between terrain conditions and various factors,and provide reference for the design of UHVDC transmission lines and the reconstruction of later lightning protection,it is necessary to carry out relevant research on the factors affecting the lightning shielding performance of UHVDC transmission lines.The main work of this paper is as follows:(1)Based on the similarity between the discharge gap and the natural lightning discharge in the discharge process and the discharge parameters,the equivalence of the model proportion,the nominal electric field of the DC line,and the electric field of the descending pilot near field was studied.According to the research on the effect of model ratio on the performance of transmission line lightning shielding simulation test,the ratio of model test is determined to be 1:30.In order to ensure that the nominal electric field distribution of the model line space is consistent with the±800kV DC transmission line,the DC high voltage generator is used.The conductor is applied with±26.7kV voltage,and a 20k?-0.3?F RC circuit is designed,which greatly reduces the inrush voltage and current amplitude at the inflow high-current side,improves the reliability of the DC pressure loop power supply,and passes the natural world,simulation test.For the calculation of the rate of change of the field intensity when the corona was generated on the surface of the lightning conductors and conductors,250/2500?s negative standard operating surge voltage wave was selected as the test voltage waveform.(2)For different ground inclination angles,simulation tests on the effect of line lightning protection performance were carried out with the lightning protection angle,conductor operating voltage,and lightning first-input firing angle as variables.The test results show that reducing the protection angle of the ground wire can significantly improve the ability of lightning protection against lightning strikes.When the tilt angle is 15°,the corresponding protection intervals of-50 and 0° are respectively reduced by 20.5%and 9.6%,compared with that at 5°.The voltage polarity of the conductor has a great influence on the lightning shielding performance of the line.Compared with the negative polarity voltage,the line shielding probability increases significantly when the conductor applies a positive voltage,and the bypass interval increases by 49.5%.(3)Established an improved electrical geometrical model considering ground tilt angle,conductor voltage,lightning first-input firing angle,tower height,wind speed,and ground protection angle,and simulated the lightning shielding failure rate of±800kV DC transmission lines.The correlations between the ground inclination angle and the protection angle of the lightning conductor and the height of the tower are analyzed.The results show that for the protection angle,the inclination angle is not more than 15°,the protection angle is not more than 10° or the inclination angle ranges from 15° to 30°.When the protection angle is less than-5°,it can meet the lightning flash density of 6.85 times/km2 ·a± 800kV DC transmission line bypass flashover rate of not more than 0.197 times/100km·a requirements. |
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