Voltage surges induced on overhead lines by lightning strokes

The paper analyses the voltage induced on an overhead line by the electromagnetic effects of the return stroke of lightning. The effects of a rectangular return-stroke current as well as currents having linearly rising front are analysed, assuming uniform charge density along the stroke channel and return-stroke velocity as a constant parameter. The analysis, which corroborates recent field data, shows that the induced voltage is not entirely a travelling-wave phenomenon. Contrary to the previous studies, this study shows that the waveshape of the induced voltage can be bipolar. Furthermore, the magnitude as well as the front time of the return-stroke current may be predicted approximately from the oscillogram of an induced voltage. The magnitudes of voltages induced by indirect strokes can exceed the basic impulse insulation level of high-voltage systems.