Effect or Preceding Bias Voltage on Switching-Surge Operation of Spill Gaps and Lightning Arresters

Line-dropping tests on the Southern California Edison Company system showed that previously encountered spill-gap operation was not caused by extremely high switching-surge voltages, but by abnornally low sparkover of bushing-mounted gaps. In some cases lightning arresters also operated at abnormally low switching-surge voltages. Laboratory tests showed that a nonuniform gap field and trapped charges on the adjacent porcelain surface rendered spill-gap sparkover susceptible to wave front steepness and, particularly, to preceding voltages of opposite polarity. A gap located remotely from porcelain surfaces was found to be relatively free from these effects.