Calculation Research on the Distance Between the Grounding wire and Conducting wire of the Middle Span for ±800kV Transmission Lines

-For overhead transmission lines, the insulation coordination of the grounding wire and conducting wire depends on the size of tower-head and the minimum safe distance between the grounding wire and conducting wire of the middle-span, which is related to the lightning current steepness, the length of the span, and the coupling coefficient between the conducting wire and grounding wire, etc. GB 50790-2013 〈Code for designing of ± 800kV DC overhead transmission line〉(In Chinese) points out that the distance between the grounding wire and conducting wire of the middle-span should be determined by mathematical computation, but does not give exact computation method, only a suggested formula is given in the appendix, which does not consider the influence factors such as the lightning current steepness, the coupling coefficient between the conducting wire and grounding wire, and so on. For this reason, this paper introduced a method named wave processing analysis (WPA), to make up for the shortness of the formula suggested by GB 50790-2013. To prove the rationality of WPA method, the distance between the grounding wire and conducting wire of the middle-span for a ±800kV UHVAC transmission project has been computed by those two methods mentioned above. Results showed that the distances obtained by the suggested formula does not satisfy the requirement of lightning withstand level, while WPA method can consider this requirement, so WPA method is a better method to determine the distance between the conducting wire and grounding wire of the middle-span. The calculation principle of WPA method can also be used to calculate the distance between the grounding wire and conducting wire of the middle span for other voltage level DC &AC transmission lines.