Power System Blackouts - Minimizing their Impact at Industrial Co-Generation Facilities

Investigations of recent blackouts indicate that the root cause of almost all major power system disturbances is voltage collapse rather than the underfrequency conditions prevalent in the blackouts of the 1960s and ´70s. This paper explores the nature of recent power system blackouts (2003 east coast, 1996 California and others) and explains why voltage is the leading edge indicator of impending power system collapse. The paper discusses the need to use voltage - as well as frequency - to decide when to separate from the utility system and transfer industrial system load to internal plant co-generation. Industrial customers have used voltage relays to determine that the utility circuit that supplies them has tripped. However, voltage relays at industrial sites have generally not been used to determine that the utility system lacks security and may collapse. This paper discusses the causes of voltage collapse as well as the design and security requirements for an undervoltage separation scheme. The paper addresses the current level of voltage load shedding on utilities´ systems, NERC (North Electric Reliability Council) requirements and coordination of industrial undervoltage separation with utility undervoltage load shedding.