The security of a bulk power system is threatened when it is loaded near to its maximum capacity. Voltage instability and undesirable protective relay operation are two major interrelated phenomena that can occur when the system is under stress. As reported in many voltage collapse incidents, when the system is subjected to a major disturbance, high loading conditions on system components tend to operate protective relays. The operation of these relays further trips the critical components, leading to cascading events of tripping. The lack of reactive power during heavy loading conditions may trigger field limiters and overload protection to trip the generators. Undoubtedly, this directly contributes to wide-area blackouts. There is a need for countermeasures that take into account both system wide disturbances as well as undesirable protective operation. The amount of corrective control needed to save the system from voltage collapse depends on the timing of the control. The amount of required control increases dramatically if the timing of the control is beyond the critical time. A cost effective control strategy is need to determine when, where and how much control is needed to avoid system wide collapse. The proposal directly addresses these issues in a comprehensive and coordinated way. The framework includes a novel decoupled manifold-based time-domain simulation algorithm to identifying system collapse. A novel optimization-based control determination algorithm then provides the location, the quantity, and the timing of control to avoid system collapse.
