Taking Into Account The Distribution Network Load Reduction Strategy And Line Breaking Current Limiting Strategy In Emergency Situations

The cascading failure caused by a single fault in the power system will frequently cause blackouts.Often from a single part of the failure to a cascading failure causing the entire network to collapse,dispatchers and supervisors have no time to take effective control.measures to prevent further spread of the failure.Therefore,it is necessary to grasp the operation status of the power grid in advance,improve the reliability of the distribution network,and take protective measures in advance to avoid cascading failures and ensure the stable and safe operation of the power system.Based on the strong and weak connection state of the distribution network,and considering the dynamic equivalent method of the modified network and the current limiting sensitivity of the branch,this paper proposes a distribution network load reduction strategy and a line breaking current limiting strategy under emergency conditions.(1)First,study the strong and weak connection state of the distribution network.Then the system is divided according to the strong and weak connection state of the distribution network,and an improved node labeling method is proposed that combines the advantages of the semi-dynamic method and the dynamic method of labeling.The less outgoing degree is,the higher the matrix sparsity is,and the more outgoing degree is,the lower the matrix sparsity is,that is,the partition can be divided according to the sparsity of the node admittance matrix,and then a dynamic REI equivalent model added to the modified REI network is established to match The external network of each partition of the electric system is simplified by REI equivalent,which is used as the basis for the following.(2)Then,it is proposed to carry out independent load shedding for each partition,and when the branch power flow of the power system crosses the boundary,the sensitivity of the power of the crossbound branch to the injected power of the node is obtained.Obtain the high sensitivity within the preset sensitivity range,and obtain the load shedding range of the power distribution system according to the cross-border amount of the cross-border branch corresponding to the high-sensitivity and high-sensitivity nodes,and then according to the obtained load shedding range The load shedding model is established,and the load shedding amount of the power system is finally obtained.The conventional load reduction model is compared with the optimal load reduction model with local optimization and correction in the partition,and it is found that the network scale of the improved optimal load reduction model is smaller,thus saving a lot of computing time.The IEEE RTS79 and IEEE RTS96 standard node example also illustrates the effectiveness of the method proposed in this chapter.(3)Finally,the idea of pre-processing the original system by using the sensitivity of branch current limiting is proposed.The system is divided into a main system and several external subsystems,and then an equivalent model of REI added to the modified REI network is established to simplify each subsystem.The current limiting sensitivity of a single exceeding-standard node is extended to the current-limiting sensitivity of multiple exceeding-standard nodes.Finally,the current limiting sensitivity analysis of the IEEE39 system after dynamic equivalence is done.The disconnection current limiting strategy based on the dynamic REI equivalent method proposed in this paper saves the steps of the traditional method that requires the whole network search and traversal disconnection measures.The current-limiting branches are pre-processed once before the selection of the distribution system,which saves a lot of time.Finally,an example of IEEE39 standard node is used to prove the effectiveness of the method proposed in this chapter.