Lightning Protection Performance of Back-flashover for Quadruple-circuit Transmission Line with Dual Voltage 1000 kV/500 kV on the Same Tower

Mixed-voltage multi-circuit transmission line on the same tower can be considered in UHV grid in eastern China where the area for the line corridor is limited.It is of great significance to study the back flashover performance of the UHV mixed-voltage multi-circuit transmission lines on the same tower(UMMTL).Consequently,taking the influence of the working voltage into account by using statistical method,basing on PSCAD/EMTDC,we established a simulation model of the back-flashover performance for quadruple-circuit transmission line with dual voltage 1000 kV/500 kV on the same tower.Compared with the conventional lines,characteristics of the back-flashover performance were summarized for UMMTL.With the consideration for the specific characteristics,the influences of the insulation level of the lateral conductor,one side conductor of the 500 kV upper layer cross-arm and the phase arrangement for 500 kV lines on the back-flashover performance were analyzed.The results show that the back-flashover trip-out rate of the single circuit and the double-circuit for 500 kV lines both decrease when the insulation level of the lateral conductor is enhanced.The back-flashover trip-out rate of the double-circuit for 500 kV lines decreases when the insulation level of the one side conductor of cross-arm is improved.The back-flashover trip-out rate of the single circuit for 500 kV lines is comparatively higher than that of the double-circuit when different phase conductors are used for lateral conductor.Thus the back-flashover performance for 500 kV lines can be improved by enhancing the insulation level of the lateral conductor.The back-flashover performance for 500 kV double-circuit lines can be improved by enhancing the insulation level of one side conductor for upper layer cross-arm,and with the implement of unbalanced insulation as well as different phase conductors for the lateral conductor of 500 kV lines.