Arc motion and burn through in GIS

It is pointed out that two different mechanisms are effective for the burn-through process of GIS (gas insulated substation) encapsulation by an internal arc during an in-service fault: the material erosion by melting and evaporation and the weakening of the material by heating. Depending on the arc motion one of these mechanisms may be dominant. Hitherto inexplicable motions of the arc are explained; especially the arc rotation at a spacer and the axial motion in case of symmetrical current feeding. These considerations are confirmed by experimental results and experience from industry, and they result in some recommendations for the design and the protection concept