Transmission line switching surges

RECENT IMPROVEMENTS in arrester impulse protective levels have permitted the application of power apparatus having insulation reduced two voltage classes on well-grounded systems where 75% or 80% arresters can be applied. Although the insulation of such apparatus can be adequately protected against impulse voltages, the adequacy of lightning arresters to protect the reduced insulation against switching surges is not so well established. Some of the areas receiving increased attention by the electrical industry are: 1. Determination of magnitude, wave shape, and duration of switching surge voltages. 2. Establishment of the insulation strength of apparatus subject to switching surge voltages. 3. Determination of the duty that arresters will be subjected to in providing protection for apparatus when exposed to excessive switching surge voltages.