Wide-area Information Based Research On Flow Transferring

Flow transfer is the main factor which causes the mis-operation of back-up protection, especially overload protection and distance zone III. Therefore, the influence of flow transfer must be eliminated as soon as possible, otherwise, may lead to cascading outages. If the reason of overload on lines is identified as flow transfer, generation rescheduling and load shedding would be considered to lead the system to the normal state in the condi-tion of the minimum load loss and the propagation of cascaded events could be prevent completely.Linear coefficients which can respond the change of the real power flow in all lines with respect to a change in the injection at all buses are presented. Based on these, the reason of overload on lines can be identified by a criterion which is presented in this paper. In a word, when the mis-operation of back-up protection due to flow transfer occurred in power system, the back-up protection can be blocked by the criterion. However, the power system is also located at emergency operation state.According to the linear coefficients which can respond the change of the real power flow in all lines with respect to a change in the injection at all buses, generation and load can be separated into a"raise"generation list, a"lower"generation list and a"shed"load list, and the rescheduling trend of the generation or load in each list would be same when any overloading condition has been checked.Secondly, the sum of generators'positive outputs, negative outputs and load shed-ding are optimized using particle swarm optimization (PSO). Thirdly, the sum of positive output, negative outputs and load shedding are rationally distributed by assorting genera-tors and load shedding nodes; and the corresponding flow transferring control strategy is formed aiming at accurately controlling of flow transfers in the system. This method can precisely adjust and control line overloads due to re-sectioning of single branch or multi-ple branches in a simple and rapid way. The simulation demonstrates that the control strategy is effective and scientific.