The Potential Distribution Of ±500kV DC Tension Tower And Detection Of Lightning Current

The DC line lightning failure statistics shows that tension tare strike tripping times accounted for 40% of the total number of lightning trip-out. Therefore the lightning-shielding transformation of HVDC lines has become an urgent problem. In the reform of the lightning protection, the shape of the insulator structure features and characteristics of the material with high resistivity makes uneven electric field intensity and potential distribution of insulator surface and easy to cause insulator aging. So the research about potential distribution of insulator string after lightning-shielding transformation is of great importance for maintaining security and stability of transmission line. At the same time, in view of the lack of a real lightning current parameters in the lightning-shielding transformation of transmission line in current domestic that mainly through simulation experiment,theoretical analysis and research, as a result, the research about lightning current detection system has a great significance to the improvement of lightning-shielding transformation.This paper firstly analyzes the potential distribution of insulator string in the lightning-shielding transformation of ±500k V DC tension tower, and optimizes the sharing ring to the finite element method. Then the potential distribution of insulator string is analyzed when the transmission lines are struck by lightning with ATP(The The Alternative Transients Program). The lightning current detection device based on FPGA is designed in order to collect the lightning current waveform. Finally, the influence factors of shielding effectiveness of shell of lightning current detection system is analyzed using the finite element method in order to avoid lightning electromagnetic pulse damage the electronic components inside the system. The main content of this paper includes the following aspects:(1) The three-dimensional electric field computation model contained tower,divided conductor,equalizing ring, lightning arrester, hardware and insulator string for ±500k V DC tension tower is established based on Ansoft Maxwell, This paper analyzes the impact of lightning arrester and equalizing ring on suspension string potential. The reasonable structural parameters of the uniform ring is ascertained.The results show that, lightning arreste and equalizing rings have an important influence on the potential distribution of suspension string. The potentialdistribution and electric field distribution of insulator string become more uniform by the optimization of structural parameters of the sharing ring in high and low voltage side, but also the optimized sharing ring can restrain the impact that over-voltage have effect on the three dimensional electric field of insulator string.(2) This paper establish the transient analysis model of potential distribution of insulator string and study potential distribution with ATP when lightning struck the transmission lines, tower or central span of ground wire. This paper also analyzes that the grounding resistance have an effect on lightning withstand level. As the result show that the potential differences of insulator string when the transmission lines are struck by lightning is higher than the other cases, and the grounding resistance have a great impact on the lightning withstand level.(3) In order to collect the lightning current waveform, this paper developed a set of lightning current detection device based on FPGA. The hardware of device adopt modular designer and is mainly composed of data acquisition unit, data processing, data storage and data communication. The software of lightning current detection system is designed with SOPC. The device not only has 8 bits sampling size, but also data length collected by device is 200 us. Experimental results show that the trigger pulse waveform detedted by the device consistent with the waveform generated by signal generator, and the trigger pulse waveform cover the total wave front time and wave tail time.(4) The paper sets up the simulation model of shielding effectiveness analysis of the lightning current detection system by using Ansoft Maxwell, and studys the influence of the material type of shield, the shield thickness and hole size and location on the shielding effectiveness. The analysis shows that generally completely mental box has high shielding efficiency, while the air hole can greatly damage the shielding effectiveness. So the system and the signal transmission cable and its interface must take the necessary shielding measures in order to reduce the lightning impulse coupling interference.