Application of Non-Gapped Line Arresters to 150 kV and 400 kV Overhead Lines: Effects of AC Voltage at the Instant of Direct Lightning Strike

This study investigates the effects of the AC power-frequency operating voltage instantaneous value when lightning strikes to an overhead transmission line (OHTL) on the computed fast-front overvoltages across insulation, the current flowing through line surge arresters (LSAs), and the energy absorbed by LSAs. The investigation is performed via ATP-EMTP simulations of two typical 150 kV and 400 kV OHTLs with two circuits per tower, equipped with non-gapped line surge arresters (NGLAs). Two NGLA configurations are studied: 3 and 6 NGLAs installed at all towers. Simulation of lightning strikes to phase conductors (shielding failure) and to towers are carried out for negative first return strokes. The tower ground resistance at low current and low frequency is a parameter in simulations; ground resistance values are selected among those commonly encountered in practice. It is found that there is a significant variation of NGLA absorbed energy depending on the power-frequency voltage value at lightning strike time instant. An enhanced variation is observed for the 400 kV OHTL. Hence, the worst-case conditions in terms of power-frequency voltage should be considered for NGLA energy withstand capability selection.