Analysis of switching surges on a 220-kv line

IN RECENT YEARS, improvements in lightning arrester characteristics have permitted reductions in transformer insulation levels and have led to extensive analysis and investigation of switching surges. Before the common use of reduced BIL transformers, switching surges were of no concern in most cases, since their magnitudes were well below the insulation strength of the windings. As transformer BIL is reduced, however, normal switching surges become a factor and arresters may be universally required for complete protection.