Study the Induced Voltage Caused by Lightning Flash to Overhead Power Lines Tower

To estimate overhead lines lightning performance, the back flashover critical current computation of insulators is important. There are two methods at present. One method counts for the surge response at cross-arm and shielding wires, also shielding wires inducing voltage on phase lines. The other method not only considers the above components, but also counts for the lines induced voltage caused by the lightning electromagnetic field. The two methods produce great differences for the same lines. Many studies have proved that overhead lines induced voltage caused by lightning flash to their nearby ground be high, the biggest induced voltage reaches to or exceeds its operation voltage a few times. As lightning flash to tower, because the lightning return stroke channel or lightning striking point is near to the considering lines, its induced voltage will be accordingly higher than that produced by indirect lightning striking to nearby ground. This paper analyzes the lightning current distribution in the lightning channel and the transmission tower when lightning flash to a tower top. It is found that the great lightning current is reflected to the lightning channel because of the reflection effect at the tower top. When the tower is higher, the lightning striking point is far away from the ground. Based on the electromagnetic field theory, the induced voltage on the same height overhead lines is small since big lightning current is far away on the tower top. Using numerical electromagnetic code and its coupling to lines modeling, the overhead lines induced voltages are computed. The simulation results show that, sameness to the indirect lightning, the influence action of lightning striking distance is transformed to the tower up-leader height. That is, the lines induced voltage caused by lightning striking to tower top not only relates to the lines height, but also relates to the tower height.