Heading off emergencies in large electric grids

Until recently, power systems in the United States could be counted on to operate reliably. For more than half a century, generating and transmission reserves were ample enough to absorb constant increases in the consumption of electricity. But in recent years, that growth has combined with two other trends-larger than ever bulk transfers of electricity over ever wider areas-to subject power systems to operating conditions unanticipated during their original design. Here, the authors describe how the blackouts that swept power systems in the Western USA in 1996 could have been prevented by the use of a centralized automatic response system.