Study On Flow Transferring Identification Considering Multi-line Tripping And Overload Control Strategies

Flow transferring caused by the elimination of initial fault leads to the restbranches in system especially those closely related to the point of failure overload,which will cause cascading trips of the backup protection. So the effect on powersystem caused by elimination of the fault or element out of operation must bevalued, if necessary the corresponding control strategy should be carried out.In order to quickly identify flow transferring in real time,flow transferringidentification is expanded from a single line tripping to multi-line tripping,linetripping distribution factors based on DC power flow and compensation principle isdeduced to estimate the distribution of multi-line tripping power flow quickly,thencombining with the improved severity function, the concepts and solving process ofkey branch set and overload risk indicator used to estimate impact of flowtransferring are introduced in detail,which can apply to single line tripping andmulti-line tripping equally and reduce analysis range of subsequent load sheddingcontrol strategies.The example analyses of10-generator39-bus New England Systemshow that the method can estimate tripping power flow accurately,identify thebranches severely affected by flow transferring quickly and efficiently,overcome thedeficiency of using distribution factor to evaluate flow transferring degree andmiss-selection of important branch.On the basis of flow transferring identification, sensitivity calculation models forsingle line tripping and multi-line tripping are introduced, single line overload controlstrategies based on the generalized sensitivity and key branch set are studied,in whichimportant load proportion on the the control node is considered. The exampleanalyses of10-generator39-bus New England System show that the method caneliminate the overload with minimum adjustment quantity, guarantee the continuoussupply for important load,and ensure no overload of other branch.The depth first search algorithm and the theory of electrical dissection are combined to form subdivision algorithm for overload branch, control nodes are thosein the generator nodes set and load nodes set which have the supply anddemand relationship with overload branch,control nodes occupancy ratio of overloadbranch power and load power supplied by the generators in generator nodes set areconcluded. On this basis, multi-line overload control strategies are studied based onelectrical dissection algorithm. Example analysis results show that the strategy caneffectively eliminate the multi-line overload with minimum adjustment quantity, andit do not need multiple iterations, thus the strategy introduced can effectively preventcascading trips.