Insulation Configuration And Performance Analysis Of UHV DC Transmission Lines

The insulation of the UHV DC transmission line configuration has a great impact on the running level and transmission capacity of transmission line.Because the voltage level is very high,the transmission capacity is particularly large,the transmission distance is particularly long and so on,once the UHV DC transmission line insulation failure,serious economic losses and strong system instability will be caused.In addition,the high voltage DC transmission will produce"electrostatic adsorption effect",so the insulator surface pollution is more serious,while the DC insulator surface flashover characteristics and communication are very different.The above factors make high voltage DC line pollution more serious,while flash discharge accident and ACwith the voltage level of the transmission line is more obvious.Therefore,it is very important to improve the operation level of the system by selecting the insulation configuration of the DC transmission line reasonably.In this paper,combined with the actual operation of our country and the number of ± 800kV UHV DC transmission lines under construction,the design and configuration of insulation are discussed and learned from the following aspects,and the design advice of ± 800kV UHVDC transmission line tower head air gap and insulation configuration are given:(1)Through the analysis of DC discharge characteristics,switching impulse discharge characteristics,lightning impulse voltage effect on air-gap,wind-age,elevation and other factors,the insulation configuration is designed for tower-head air-gap combined with the corresponding test.Through the experiment research combined with high voltage and ultra high voltage line operation experience,we can obtain that the power frequency voltage and lightning impulse voltage of air gap in the tower-head of HVDC transmission line insulation configuration is not the decisive factor,while the operating voltage impulse voltage and line is directly related to the key factors of tower head insulation configuration design.Due to its flexibility and diversity,the live mode is less likely to be the control factor of the gap size of the line insulation.Under different altitudes,the line should be revised according to the standard meteorological conditions.When the different insulator strings are used,the air breakdown channel of the tower-head is different,and the distance between the tower and the tower-head is different,which is the factor that must be considered when designing the air insulation.Therefore,reasonable selection of air-gap switching impulse voltage and charged operation,as the main basis of the design of the tower-head,to ensure the safe operation of the ±800kV UHV transmission line and line maintenance,effective control of the project cost is very important.(2)This paper analyzes the performance characteristics of the DC line insulators and provides suggestions on the selection of insulator for UHV DC transmission line combines with the performance and characteristics of the composite,porcelain and glass insulators.In general region,according to the regional pollution degree,the tension strings generally use porcelain or glass insulators,and suspension string can reasonable use the composite insulator or glass insulator.In the region of heavy ice,for the insulation performance of composite insulator is decrease seriously,generally use porcelain or glass insulators.In high altitude region,suspension string generally use composite insulator,tension string generally use the porcelain insulator,or glass insulator.(3)With taking Shanxi Jinbei-Jiangsu Nanjing project as an example,the selection of insulator strength is dicussed.At the same time,creep-age distance method,the law of the tolerance of pollution,±500kV insulator level extrapolation method are applied to analyze the selection of the insulator string length of ±800kV UHVDC transmission lines.Considering the long-term exposure to the natural environment of UHVDC transmission lines,the surface salt density,the ratio of the gray density and the distribution of the pollution of the upper and lower surface of the insulator have been uneven,and all of them have been modified.At the same time,because UHVDC transmission line path is long and terrain environment is complex,there is a big difference along the altitude.The determine of the length of the insulator string should consider influence of the altitude and perfect the design.(4)The pollution level distribution along the Jiangsu Nanjing DC line is recommended in the paper,which based on division of AC pollution area in north and central of China(mostly in Shandong province),the natural geography and climate characteristics of Shanxi Jinbei-Jiangsu Nanjing project,and each section of the contamination and wetting characteristics,adjacent AC and DC transmission lines ESDD measurement results are conducted a comprehensive survey and analysis.The proportion of the total line length of DC light,neutral?heavy polluted area were 0%,32.9%and 67.1%respectively.According to the above aspects,the description of the insulation configuration of Shanxi Jinbei-Jiangsu Nanjing project presents an effective practical calculation and insulator selection of the engineering practice of ±800kV UHVDC transmission lines.