Flashover vulnerability of transmission and distribution lines to high-altitude electromagnetic pulse (HEMP)

The vulnerability of transmission and distribution lines to flashover from the electromagnetic pulse generated by a nuclear detonation 400 km above the Earth is estimated. The analysis consists of determining the cumulative probability of induced voltage on three-phase lines, including shield and neutral conductors, for four operating voltages and then comparing these stresses to estimates of line insulation strength. The 12 kV line is shown to be vulnerable to HEMP-induced flashover. The 69 kV line is marginally vulnerable to HEMP-induced flashover, but only the minimum-insulation designs in current use are susceptible, and the probability of flashover for those designs is minimal. The 500 and 230 kV lines are invulnerable to HEMP-induced flashover for all HEMP field levels considered