Study On The Lightning Shielding Performance Calculation Model For The HVDC Transmission Lines Considering The Operation Voltage

In recent years, lightning stroke is one of the important causes of the accidents that occur on transmission lines. With the increase of voltage grade of transmission line, the proportion of outages because of shielding failure also increases. Therefore, exactly evaluating lightning-withstanding level and shielding failure flashover rate (SFFOR) of transmission line is especially important for system service and stable operation.As the increasing of HVDC transmission projects in China, the lightning shielding performance of the HVDC transmission lines is also one of the especially important aspects which restricts the service and stable operation of a HVDC transmission system. The operation voltage of HVDC transmission lines is an invariable DC voltage; and along with corona izons caused by the invariable DC electric field distributed in the vicinity of the lines, the lightning shielding characteristics of HVDC transmission lines have a"polarity phenomenon"which is different to that of the AC transmission lines. Therefore it is not adequate to evaluate the lightning shielding performance of the HVDC transmission lines by using the anlasys methods which are carried out before.The physical approach of electric geometry model (EGM) is discussed here, a new electric geometry model concerning the operation voltage is introduced based on the argumentation. Applying this model, the lightning shielding performance of±500kV and±800kV HVDC transmission lines are calculated here, the calculation results indicate that: under the same geometry configuration of transmission line and insulation level, the maximum shielding failure current of the positive polar is 1.3~1.7 times higher than the results which is not considering the operation voltage.The existing leader progression models (LPM) are analysised here, and based on the observed lightning and spark discharge data, a new numerical model for the lightning shielding performance of the HVDC transmission lines is presented, which considering the main approaches of the earth flash, such as: the progression of descend leader, the inception of upward leader, the relative development of the descend leader and upward leader and the final jump. The calculation results based on the numerical model present here is in accordance with the 1:40 scale test results carried by Wuhan Univercity. The calculation results indicate that: for a negative earth flash, the positive operation voltage increases the lightning attractive ability of positive polar conductors, and restrains the lightning attractive ability of grounded wire at the same side.