Operating under stress and strain [electrical power systems control under emergency conditions]

In the U.S. today, complex power systems are able to provide reliable electric service at low cost with the help of automatic control - simultaneously tracking the randomly varying system load, optimizing generation to minimize cost, and coordinating the action of many independent control centers. When an emergency develops in one of these systems, however, the picture changes completely and new control objectives must be met if the system is to be restored successfully to normal operation.