Impulse and Dynamic Flashover Studies of 26-Kv Wood Pole Transmission Construction

This paper presents the results of a series of laboratory tests made with a million volt surge generator and 60-cycle high-voltage testing equipment on unit pole transmission construction now in standard usage on a large 26-kv transmission system. Actual impulse curves are given for several types of straight span pole top construction. Basic values of impulse flashovers are presented which should facilitate coordination of impulse insulation between poles of any similar transmission lines, aid in applying protective gaps, and furnish a guide to the comparative impulse strength of both present and new types of construction. Defects in present design standards and possible improvements are discussed. An analysis of the factors governing the development of a power arc following impulse sparkover and corresponding experimental data showing the extent of occurrence of such arcs are presented. The paper concludes that reliance upon air or wood separations within the usual physical limits to prevent lightning outages will be unsatisfactory, and discusses the application of protective measures.