Study On Lightning Protection Performance Of Quadruple-circuit Transmission Line With Dual Voltage 1000kV/500kV On The Same Tower

With the planning and construction of UHV grid in China, UHV mixed-voltage multi-circuit transmission lines on the same tower (UMMTL) can be considered in UHV grid in eastern area where line corridor is tensional. The tower's height and volt-age level of UMMTL is comparatively higher, the transmission line on tower has two voltage level, so the lines are suffered by lightning stroke easily. Compared with the traditonal lines, whether there are the own characteristics of UMMTL needs to be stud-ied, the other problem is whether the methods applied in traditional lines is still avail-able for UMMTL. Therefore, it has important scientific significance and practical value to research the suitable methods for analysis of lightning protection performance of UMMTL and carry out the research of lightning protection performance for UMMTL. This paper discussed the lightning protection performance of quadruple-circuit trans-mission lines with dual voltage 1000kV/500kV on the same tower systematically.According to the features of quadruple-circuit transmission lines with dual voltage 1000kV/500kV on the same tower, simulation model for lightning protection perform-ance of back striking which considers working voltage is established based on PSCAD/EMTDC. The traditional EGM is improved in this thesis, the exposed distance of transmission lines under different lightning invasion angles is used to discripe the shielding failure of lines, the formula of exposed distance under different lightning in-vasion angles is proposed, the improved EGM suitable for researching lightning protec-tion performance of shielding failure for multi-circuit is built, and it also considers the influence of working voltage.Lightning protection performance of back striking and shielding failure for UMMTL is researched based on the models, comparative analysis is carried out be-tween UMMTL and conventional lines, characteristics of lightning protection perform-ance for UMMTL are summarized: back flashover trip-out rate for single circuit and double-ciecuit of 500kV lines is comparatively higher, back flashover trip-out for single circuit can easily develop into back flashover trip-out for double-circuit, the critical facter leading to back striking is the upper layer conductor of 500kV lines; shielding failure trip-out rate of 1000kV is comparatively higher, lines of two voltage level can be shielded and protected by each other, the key of lightning protection of shielding failure is the second layer conductor of 1000kV lines. According to the features of lightning protection performance of back striking and shielding failure for UMMTL, different factors are analyzed, the results indicate that back flashover trip-out rate of single circuit for 500kV lines is comparatively higher and double-circuit is comparatively lower when different phase conductors are used for lat-eral conductor (7,10) of 500kV upper layer crossarm. Back flashover trip-out rate of single circuit and double-circuit for 500kV lines decreases with the insulation level of lateral conductor or upper layer conductor enhanced. Lightning withstand level of back striking for single circuit and double-ciecuit does not change with the enhanced insula-tion level of medial conductors (8,9). Back flashover trip-out rate of double-circuit for 500kV lines decreases with the enhanced insulation level of one side conductors (7,8) of crossarm. The insulation level of upper layer conductor can be enhanced to improve lightning protection performance of back striking for 500kV lines. In order to improve lightning protection performance of back striking for 500kV single circuit, the insula-tion level of lateral conductor can be enhanced. In order to improve lightning protection performance of back striking for 500kV doublie-circuit, different phase conductors should be used for lateral conductor of 500kV lines, the insulation level of lateral con-ductor or one side conductors for upper layer crossarm can be enhanced, unbalanced insulation can be used. Withθs, H and l1 increasing, shielding failure trip-out rate of 1000kV lines and whole lines increases. Shielding failure trip-out rate of 500kV lines is unchanging and then decreases with the increase of l1, decreases and then increases with the increase of H and is unaffected byθs. With l2 increasing, shielding failure trip-out rate of 1000kV lines decreases, 500kV lines and whole lines increases. In order to im-prove lightning protection performance of shielding failure for UMMTL especially for UHV lines,θs can be reduced and l2 can be increased appropriately in the range of 20.06-25.06, drum arrangement and umbrella arrangement of transmission lines should not be used for UHV lines, l1 or H can be minimized on the premise of meeting insula-tion requirements.