AC network centennial years of distribution networks

Automatic AC secondary distribution networks are the norm in urban areas of dense load concentration; no electrical distribution engineer could imagine any other technique. A century ago, dc distribution predominated in such urban areas. Alternating current distribution was minimal, with radial feeders from transformer substations to the local transformers that supplied customers. It was not as efficient or reliable as dc and lacked battery backup. Direct current distribution systems were expensive, and ac promised a potential 500% reduction in distribution costs by elimination of the substations and heavy cables required by dc systems if reliability and efficiency could be improved. © 2003-2012 IEEE.