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Power systems must be operated within limits that will ensure adequate generation and transmission capacity to avoid cascading. In developing a set of operating limits, it is important to do so within a general framework in order to ensure that the operating objectives are met. In this regard, a set of general guidelines are presented below: 1. The integrity of the transmission system will be maintained at all times without planned internal separation. 2. Maximum reasonable assistance will be given to adjacent systems experiencing difficulty. However, such assistance will be terminated - without opening interconnection circuits - when the reliable operation of the assisting system is impaired. 3. The system should be operated so that the occurrence of the next single contingency (outage of tower, circuit, unit, breaker, bus, etc.) will not result in a cascading loss of the bulk transmission system. The single contingency is continually geared to the current state of the system and reflects maintenance and forced outage events as they occur. In addition, when evaluating overload contingencies, the time to relieve the stress must be compared to the permissible degree of overload. 4. When the system experiences a generation-load imbalance, the principles of sound interconnected operation will be maintained by bringing under control an unscheduled tie-line power flow condition as quickly as possible.
Horowitz et al. (1971) studied this question.