The Research On Power System Cascading Failure Mechanism And Risk Assessment Method

In recent years, a series of cascading large blackouts have occurred in some countries, which caused huge social economy loss. When cross-region power network in our country is accomplished, cascading failures will possibly become a new question that endangers power system security. Therefore, both the full understanding of cascading failures mechanism and the deep study of related research area are beneficial to both form reasonable network configuration and implement corresponding preventive measure.The dissertation studied a search method for system state, a risk evaluation of circuit breaker open-failure, a continual fault evolution model and a probabilistic risk assessment method for cascading failure.A conclusion was derived from general physical process of cascading failures. According to characteristic of stages in cascading failures, a guiding principle of research on cascading failures was proposed.A search method for system state was studied, which aimed at slow continual outage stage. First, element fault models which possibly appear in this stage were summarized. Because element fault models are involved with configurations of power network and substation, the method must coordinate relations among fault models; guarantee both integrity and uniformity of them. This goal has been realized by use of function group decomposition and event tree analysis technique.The resist-operation on breaker was specially discussed. The preliminary risk assessment on breaker mal-operation with different electrical main wirings in normal operation way was brought forward. The result indicated that the risk of double bus four segment connection or double bus four segment connection with bypass is smallest; whereas that of single bus bar, bridge connection, or angle scheme is biggest.In view of fast continual outage stage, a continual fault evolution model used to study cascading outages for electric transmission equipment's over load was proposed. Based on temporal reasoning thought, the model proposed fault path search strategy considering time sequence, which enabled the model to have temporal characteristic.Finally, a probabilistic risk assessment method for cascading failure of power system was introduced. Dispatch and maintenance staff can obtain different risk indicators to prevent possible cascading failures by use of this method. Simulation also indicated that if the probability of resist-operation on breaker is the same magnitude as that of misoperation of protection, the former is more dangerous. Bus configurations of power station and substation have an influential role in cascading failures research, which may display through open-failure of breaker.