They keep enough distance between each line so  that electrical arcs can't form between them.

它们在每条线之间保持足够的距离，以便它们之间不会形成电弧。

When  this impulse reaches the fault, it causes an electrical arc which can be heard as a thump above  the ground, usually aided by a handheld detector with a microphone and digital filters.

当这种脉冲到达故障时，会产生电弧， 可以听到地面上的重击声，通常由带有麦克风和数字滤波器的手持探测器辅助。