Back flashover's lightning performances for 500 kV AC transmission lines with quadruple-circuits on single tower

Lightning performance calculation and analysis of back flashover for 500 kV AC transmission lines with quadruple-circuits on single tower was obtained by electromagnetic transients program (EMTP). Lightning performance influenced by different factors such as grounding resistance, height of tower, and grounding wires was calculated and analyzed in details. Electric potential waveshapes of tower body and crossarms were presented by EMTP, also voltage waveshape between upper or lower crossarms and any given phase conductors. Under the lighting stroke, electric potential of tower body reduces gradually from top to down while that of the top crossarm reduces gradually from one side with lightning stroke to another side without lightning stroke. Voltage everywhere of the middle crossarm is almost same, also of the down one. Voltage between phase conductors and upper crossarm is higher than that between the phase conductors and lower crossarms. As a conclusion, measures to reduce damages brought by back flashover are listed below: reducing height of towers, setting up grounding wires in the center of the top crossarm and both sides of the second crossarm; increasing the air gap distance between phase conductors and their the upper crossarms, etc.