A flashover is a breakdown in which an arc bridges an insulator or air gap, usually from a live conductor to earthed metal or between phases. Lightning, switching surges, wet or polluted insulators, birds, animals and insufficient clearance can all set one off. On overhead lines most flashovers are self-restoring once the breaker extinguishes the arc, which is why auto-reclose works so well, but they leave burn marks on insulators and fittings that patrols look for.
Patrol found flashover marks on the top insulator at pole 47, probably lightning, the reclose held so it can wait for planned work.
Also heard as
- flash-over
Do not mix it up with
- Arc flash: Arc flash is the hazard to people from an arc; flashover names the insulation breakdown itself.
Related terms
Clearance
Straight-line air gap between two conductive parts, the dimension that decides whether a surge can flash across.
Auto-reclose
Automatic closing of a breaker shortly after a fault trip, restoring supply when the fault was only transient.
Surge arrester
Device that clamps transient overvoltages by diverting surge current to earth, then returns to insulating.
Squirrel
Control-room shorthand for an animal-caused fault, typically a squirrel or bird bridging live parts.