Analysis Of Transient Stability For Chain Grids

Grid interconnection contributes to economic and reliable operation of powersystem. Meanwhile, changes of power network structure will cause a correspondingimpact on the grid stability characteristics. This paper mainly studies transient stabilityissues appearing in the large region AC interconnection projects. The features andtransient stability characteristics of chain structure grid formed in networking project aresummarized, and then the changes of transient stability of the internal cross-section andoscillation center transfer problem after the failure of the chain structure are analyzed. Sothe transient stability mechanism of chain structure grid is explained. Factors affectingthe transient stability characteristics of chain grids are explored, which can improve theeconomy of the power system and achieve maximum utilization of the grid infrastructureunder the premise of ensuring the reliable operation of the power system.With the generator rotor equations as the theoretical basis, the thesis analyses thechanging process of variables such as bus voltage amplitude, load level, rotor angle ofboth the sending end and the receiving end system under short-circuit fault conditions,and investigates how the cascading effects brought by these variable changes lead toinstability. The law of the transient stability level change for internal sections of aregional grid after AC networking is obtained, and the process and basic mechanism ofthe oscillation center transfer of the chain type grid under faults are interpreted. It isfound that the main influencing factors of transient stability for the chain type grid arethe link strength between the subsystems and the size ratio of the different subsystems.Three machine chain system model is built by using PSD-BPA based on the resultsof theoretical analysis, and simulation analysis is focused on the influence of the scale ofeach subsystem and the link strength between subsystems on the oscillation centertransfer characteristics. The effects of the system size change on transient stabilitycharacteristics is simulated by changing the capacities of the three generators and thegenerator rotor kinetic energies, and the effects of the link strength on transient stabilityby varying line impedance. Finally, the fault verification for the interconnecting projectof the northeast grid and the north China grid is given. The practical simulation result iscompared with the theoretical analysis results and the simulation results on thethree-machine chain system. The reasons of the change of transient stability level of theinternal sections in the AC interconnected grid and the basic mechanisms of oscillationcenter transfer under faults in the chain grid are uncovered. The conclusion can provideuseful reference for grid operation and implementation of future network interconnectingproject.